Digital signal transmission system and method of displaying transmission condition in digital signal transmission system

ABSTRACT

A digital signal transmission system using a digital modulation system comprising a digital signal transmitter having a first digital signal processing unit and a digital signal receiver receiving a digital signal from the transmitter, wherein the digital signal receiver comprising a second digital signal processing unit for processing the digital signal from the transmitter and outputting a digital demodulated signal and a correlation value signal, a signal converter coupled with the second digital signal processing unit and supplied the correlation value signal therefrom for generating a waveform indicating a transmission condition including a main wave in response to the correlation value signal, and a display coupled with the signal converter for displaying the waveform indicating a transmission condition in the digital transmission system.

BACKGROUND OF THE INVENTION

The present invention relates to a digital signal transmission systemusing a digital modulation system such as orthogonal frequency divisionmultiplex (OFDM) modulation system.

In recent years, European countries, the United States of America, andJapan have already put digital broadcasting into operation or some ofthem are considering digital broadcasting. The OFDM modulation system isregarded as the most likely prospect for digital broadcasting.

This OFDM modulation system is a kind of multi-carrier modulationsystem, and is the sum of a large number of digitally modulated carrierwaves. In addition, each carrier is modulated by QPSK (Quadrature PhaseShift Keying), and the resultant wave of all the modulated carriers isthe OFDM signal.

Here, for the OFDM signal, first the QPSK signal, a_(k)(t) of eachcarrier can be expressed by the following equation.a _(k)(t)=a _(k)(t)·cos(2πkft)+b _(k)(t)·sin(2πkft)  (1)where k is the carrier number, and a_(k)(t), b_(k)(t) are data of k-thcarrier and take a value of −1 or 1.

If the number of carriers is N, the OFDM signal is the resultant of Ncarriers. If this OFDM signal is represented by β_(k)(t), it can beexpressed by the following equation (2).β_(k)(t)=Σa _(k)(t) (k=1−N)  (2)

Incidentally, in the OFDM modulation system, it is common practice toadd a guard interval to each signal unit in order to reduce themulti-path effect.

The OFDM signal is formed of those signal units. The symbol of thissignal unit is formed of, for example, 1024 effective samples plus 48samples of guard interval data, or 1072 samples. Also, a stream unitcalled frame is the sum of 892 symbols and 6 synchronizing symbols, or900 symbols in total. These stream units are repeated as the OFDMsignal.

FIG. 17 is a block diagram of the basic constructions of the modulatorand demodulator in a conventional OFDM transmission system. Thetransmission-side T_(X) construction has a transmission-side processor101 that includes a transmission path coder 1T, an encoder 2T, an IFFT(Inverse Fast Fourier Transform) 3A, a guard adder 3B, a synchronizingsymbol inserter 5, a clock oscillator 6, and an orthogonal modulationprocessor 8, and a transmission antenna A_(TX). The receiving-side R_(X)construction has a receiving antenna A_(RX) and a receiving-sideprocessor 203 that includes an AGC 9A, an orthogonal demodulationprocessor 9B, a synchronizing detector & correlator 4A, an FST corrector4B, an FFT (Fast Fourier Transform) 3C, a decoder 2R, a transmissionpath deencoder 1R, and a voltage controlled clock oscillator 10. Thesetransmission-side T_(X) and receiving-side R_(X) are connected by, forexample, a wireless transmission path L using radio waves.

The modulation and demodulation processes for OFDM signal will bedescribed with reference to FIG. 17.

Data D_(in) that is continuously supplied to the transmission path coder1T of the transmission-side processor 101 is, for example, processed foreach frame that is formed of 900 symbols. During this frame period, 894information symbols other than 6 synchronizing symbols, each including800 samples ranging from the first to 400-th and from the 625-th to1024-th samples, are processed and produced as intermittentrate-converted data D_(ii).

The transmission path coder 1T also generates a transmission-side framecontrol pulse FST at each frame of 900 symbols, and supplies it to otherelemental blocks as a frame pulse signal that indicates the start ofthose synchronizing symbol periods.

The encoder 2T codes the input data D_(ii) into data R_(f) and I_(f)that are mapped on the two axes of I and Q.

The IFFT 3A regards these data R_(f) and I_(f) as frequency components,and converts them to time base signals R (real part) and I (imaginarypart) of 1024 samples.

The guard adder 3B adds after the 1024 samples the waves of, forexample, the first 48 samples of the waves in the start period of thetime base signals R and I of 1024 samples, and produces informationsymbols R_(g) and I_(g) of time base waves of a total of 1072 samples.These 48 samples serve as a protection band when reflected waves aremixed.

The synchronizing symbol inserter 5 inserts, at every 894 in theseinformation symbols R_(g) and I_(g), samples synchronizing waves of 6symbols that are previously stored in a memory to produce data R_(sg)and I_(sg) of frames.

These data R_(sg) and I_(sg) are supplied to the orthogonal modulationprocessor 8, where they are processed by a D/A converter 81, orthogonalmodulator 82 and local oscillator 83 so that an OFDM modulated signal RFwith a carrier of high frequency F_(c) can be produced, amplified andtransmitted through the transmission antenna A_(TX) to the transmissionpath L. The transmission frequency band used is UHF band or microwaveband.

The clock CK (of which the frequency is 16 MHz) necessary to process inthe transmission side T_(X) is supplied from the clock oscillator 6 toeach block as a transmission side clock CK_(d).

The OFDM modulated signal RF transmitted as above is supplied to theorthogonal demodulation processor 9B via the receiving antenna A_(RX)and via the AGC 9A that handles high frequencies on the receiving sideR_(X). In the orthogonal demodulation processor 9B, an orthogonalmodulator 91 multiplies the OFDM modulated signal RF by a localoscillation signal of frequency F_(c)′ that is fed from a voltagecontrolled oscillator 93, thus orthogonally demodulated into the baseband signal, and then an A/D converter 92 converts it to the digitaldata R′_(sg) and I′_(sg).

These data R′_(sg) and I′_(sg) are supplied to the FFT (Fast FourierTransform) 3C, which then responds to a pulse signal FST_(rc) to producea gate signal that is used for FFT and determines the data period of the1024 samples. That is, the time base wave signals R′_(sg) and I′_(sg)are converted to frequency component signals R′_(f) and I′_(f) byremoving the 48 samples for the protection band.

These frequency component signals R′_(f) and I′_(f) are supplied to anddecoded by the decoder 2R into data D′₀, which is then further decodedby the transmission path decoder 1R into continuous signal D_(out).

The data R′_(sg) and I′_(sg) are also supplied to the synchronousdetector & correlator 4A, where a synchronizing symbol group is detectedfrom the data. Thus, the pulse FSTr is derived therefrom as a framepulse. This pulse FST_(r) is supplied to each block of receiving sideR_(X) as a frame control pulse.

In addition, this synchronous detector & correlator 4A compares thesynchronizing components of the data R′_(sg) and I′_(sg) with the clockCK_(rc) generated from the voltage controlled clock oscillator 10, andproduces a correlation output S_(c) according to the comparison result,and supplies it to the FST corrector 4B. The FST corrector 4B generatesa control voltage VC, thus controlling the voltage controlled clockoscillator 10 to generate the clock CK_(rc) with a correct period, whichis then supplied to each block of the receiving side.

Each block shown in FIG. 17 will be described in detail.

The transmission path coder 1T makes inter-leave processing, energydispersion processing and error correction code processing in order toprevent data from being erroneous due to different kinds of error thatmay be mixed during the transmission.

The encoder 2T converts the signal D_(ii) to information atpredetermined points on the I and Q axes by use of the data stored in amapping ROM, and replaces the signal of the period corresponding tounnecessary carrier by 0 to produce data R_(f) and I_(f).

The IFFT converter 3A converts the input signals R_(f) and I_(f) to thetime base waves R and I of the symbol period determined by the clockCK_(d) and pulse FST. Specifically, this IFFT converter may be thePDSP16510 made by Pressy corp. or the equivalent.

The guard adder 3B is formed of a delay circuit for delaying the inputsignals R and I by 1024 samples, and a switch for selecting only thedelayed output from 1025-th sample to 1072-nd sample. These timings aredetermined by the clock CK and pulse FST. The time base waves rangingfrom the first sample to the 48-th sample are added to the range from1025-th sample to the 1072-th sample, of the symbol that is formed ofall 1072 samples, to form information symbol R_(g) and I_(g).

FIG. 18 shows one example of the synchronizing symbol inserter 5. First,ROMs 5-1 and 5-2 are controlled by a controller 5-5 of which theoperation timing is determined by the clock CK and pulse FST, so that asynchronizing symbol signal can be generated in accordance with thetiming of the pulse FST.

Similarly, SELs 5-3 and 5-4 are controlled by a controller 5-6 of whichoperation timing is determined by the clock CK and pulse FST, so thatthe synchronizing symbol signals read from the ROMs 5-1 and 5-2 areselected only during the period from the first symbol to the sixthsymbol that is a non-signal period at the present stage, of the timebase information symbol signals R_(g) and I_(g) with guards.

Here, the synchronizing symbol signals include, for example, null (NULL)symbols for roughly finding the existence of the synchronizing symbolgroup that is in non-signal state during one symbol period, specialsymbols (hereinafter, referred to as CW symbol) having only one carrierduring one symbol period, sweep (SWEEP) symbols that are waveformschanging from the lower limit to upper limit of the transmissionfrequency band during one symbol period, and for correctly finding thepoints of symbol switching, and reference symbols indicative of phasereference necessary to delay, detect and demodulate. When 6synchronizing symbols are used, two auxiliary symbols are added to theabove symbols.

The orthogonal modulation processor 8 will be further described. The D/Aconverter 81 converts the real part signal R_(sg) and imaginary partsignal I_(sg) from digital to analog form. The orthogonal modulator 82modulates the real part signal on a carrier of frequency F_(c) fromoscillator 83, and modulates the imaginary part signal on afrequency-F_(c) carrier of which the phase is shifted 90° out of thecarrier F_(c) fed from the oscillator 83, thereby making orthogonalmodulation. These modulated signals are combined to produce the OFDMmodulated wave signal.

The operation of the receiving side R_(X) will be described. In thereceiving side R_(X), the signal of frames transmitted is supplied tothe AGC 9A, where the level of the received signal is changed to acorrect level by a control signal S_(a) internally generated. The OFDMframe signal with its level corrected by the AGC 9A is supplied to theorthogonal demodulation processor 9B.

In this processor 9B, contrary to the transmission side T_(X), theorthogonal demodulator 91 demodulates the input signal by applying thecarrier signal of frequency F_(c)′ from the voltage controlledoscillator 93, producing the real part signal, and by applying thecarrier signal shifted 90°, thus producing the imaginary part signal.These analog real part and imaginary part resulting from thedemodulation are converted to digital signals R′_(sg) and I′_(sg) by theA/D converter 92.

The synchronizing detector & correlator 4A searches for breakpoints offrames from the received signals R′_(sg) and I′_(sg) and produces theframe reference FST_(rc), and correlation output S_(c).

The FFT 3C partitions the symbols on the basis of this pulse FST_(rc),and performs Fourier transform, thus making OFDM demodulation to producedata R′_(f) and I′_(f).

The decoder 2R discriminates the data R′_(f) and I′_(f) by, for example,ROM table, and calculates data D′₀.

The transmission decoder 1R makes reverse interleave processing, energyreverse dispersion processing and error correction processing, thusproducing continuous digital data D_(out), signal S_(b) indicating BER(Bit Error Rate) status of error corrected situation, and receiving sideclock signal CK_(RX).

FIG. 19 shows one example of the specific arrangement of thesynchronizing detector & correlator 4A. Referring to FIG. 19, theorthogonally demodulated digital signals, or time base signals R′_(sg)and I′_(sg) are supplied to NULL end detector 4-1 and SWEEP calculator4-2.

The NULL end detector 4-1 detects the non-signal state or period, NULLin the synchronizing symbols from the group of symbols of frames, roughpositions (timing) of the synchronizing symbols, and estimates the SWEEPsymbol start points from the NULL end points by use of a timer circuit,thereby producing a SWEEP start command pulse ST.

The SWEEP calculator 4-2, while referring to the SWEEP start commandpulse ST, decides the waves existing 2 symbols after the NULL symbol asthe SWEEP symbol wave, receives those, and searches for the correctswitching timing of each symbol.

Specifically, a memory 4-3 in which patterns of SWEEP symbols arepreviously stored is used, and the input OFDM signal and the patternread from the memory 3-4 are processed to undergo, for example,correlation operation, and to thereby produce the correlation outputS_(c), which is then supplied to the FST corrector 4B shown in FIG. 17.

The FST corrector 4B calculates a phase shift from the correct switchingtiming of each symbol on the basis of the frame pulse FST_(r), andproduces the correct signal VC for the receiving-side reference clockCK_(r) so that the frame phase on the receiving side can be coincidentwith the transmitted data.

Turning back to FIG. 19, a frame counter 4-4 starts counting the clockCK on the basis of the SWEEP start command pulse ST, and produces apulse FST_(r) each time the count reaches a value (for example,1072×900) corresponding to the frame period, in which case the count isreset to 0, and counting of pulse CK is started.

Therefore, after that, the pulse FST_(r) is produced every constantcount, or at every frame start point. On the receiving side, this pulseFST_(r) is used as start timing for fast Fourier transform, decoding andreverse rate conversion.

The specific construction of the NULL end detector 4-1 and SWEEP startposition estimating process will be described in detail with referenceto FIGS. 20 and 21.

The signals R′_(sg) and I′_(sg) fed to the NULL end detector 4-1 areconverted to their absolute values by absolute value circuits 4-1-1 and4-1-2, and added together by an adder 4-1-3 to produce an added absolutevalue 4 a.

This added absolute value 4 a is compared with a threshold V_(th) in acomparator 4-1-4. Thus, the comparator 4-1-4 produces a compared output4 b that corresponds to the period in which the added absolute valuedoes not exceed the threshold V_(th), or the NULL symbol period betweenT₁ and T₂.

Then, an edge detector 4-1-5 detects the leading edge of the signal, orthe compared output 4 b to produce a leading edge detected output 4 c. Adelay circuit 4-1-6 delays this output 4 c by one symbol to produce theSWEEP start command pulse ST.

This SWEEP start command pulse ST is able to specify a correct SWEEPsymbol start position (T₃).

Thus, since the SWEEP calculator 4-2 can receive the SWEEP symbol wavesfrom the start, the phase shift in the SWEEP calculation can becorrectly calculated, and the correct switching timing of each symbolcan be searched for.

In other words, by detecting the phase shift by the FST corrector 4B onthe basis of the correlation output S_(c) signal produced from the SWEEPcalculator 4-2, adjusting the speed of the clock CK_(rc) as thereceiving side sample rate, and making synchronizing lock process to thephase of the transmitted synchronizing symbol, it is possible to removeerror in the FFT gate timing position. In a case that there is anyreflected wave, it is better to place the gate after the symbol period.

Incidentally, if the SWEEP start command pulse is correct in its timingposition that is determined on the basis of the detected edge of thesynchronizing symbol corresponding to rough adjustment, the FFT gate isreduced in its amount of correction for timing position that is made bythe speed adjustment of the clock CK_(rc) corresponding to fineadjustment, and thus the necessary time for the adjustment is alsoreduced. That is, the gate position can be set with error zero (noerror) in a less time, or the best decoding situation can be achieved.

Three examples of the correlation output signal S_(c) in that case areshown in FIGS. 22A, 22B and 22C. From FIGS. 22A and 22C, it will beunderstood that the correlation output signal S_(c) in that case has noreflected wave and only a sharp peak due to the main wave.

The relation of the synchronizing operation and NULL detecting thresholdin the case when there is any reflected wave will be described below.

As shown in FIG. 23, when there is any reflected wave, the NULL endpoint is detected with large error. Thus, since the detected edgeposition is delayed, the exactness of rough adjustment is reduced, andthe amount of correction for fine adjustment increases. Consequently,the necessary time for fine adjustment is increased, and it is delayedto attain the best decoding situation. If the effect of the reflectedwave is reduced, selecting the threshold V_(th) to be a lower value willmake the NULL end point due to main wave be detected with ease. Forexample, the lower value of the threshold Vth may be 30 percent of theaverage power level of the received signal. As a result, the amount ofshift at the time of rough adjustment decreases, so that the necessarytime for fine adjustment can be prevented from being extended.

FIG. 24 shows one example of the correlation output signal S_(c) in suchcase. From FIG. 24, it will be obvious that the correlation outputsignal S_(c) in this case has a peak due to main wave and another peakdue to a reflected wave.

The above descriptions were made under the assumption of high CN(carrier to noise ratio) that means the mixture of small noisecomponent. However, as shown in FIG. 25, under a low input electricfield intensity, the noise component increases, and a false signal isgenerated due to the noise component in the NULL period and mixed in thecompared result output 4 b. Therefore, the exactness of the roughadjustment may be greatly reduced. In addition, when the electric fieldintensity is further decreased, the noise component in the NULL periodalways exceeds the threshold V_(th), making it impossible at all todetect the NULL period end point. In order to assure the operation atlow CN, you should increase the threshold V_(th) to a high value. Forexample, the high value of the threshold Vth may be 80 percent of theaverage power level of the received signal.

FIG. 26 shows one example of the correlation output signal S_(c) in suchcase. From FIG. 26, it will be apparent that the correlation outputsignal S_(c) in this case includes a gentle peak due to main wavebecause much noise is contained in the SWEEP signal received on thebasis of the FST_(r) pulse reproduced on the receiving side and becausethe degree of coincidence is not increased at higher CN as compared withthat at low CN even though it is calculated while the phase in the SWEEPpattern memory 4-3 is being shifted.

While an example of the multi-carrier OFDM modulation has been describedso far, a digital transmission system of 64 QAM using a single carrierhas the same problem. JP-A-9-247128 discloses a digital signal receiverin which information of multi-path is reproduced from the receivedsignal and displayed together with the received signal level on thedisplay. However, this Japanese document teaches that the display merelydisplays the number of multi-paths and delay time of the reflected waveas the information about the multi-path (a state of reflected wave). Itis difficult to check the actual quality of the digital transmissionpath of OFDM signal only from such insufficient information. As theresult, a good quality of the reproduced image is not always obtained byOFDM modulation.

When such a digital transmission system as described above is used forradio transmission while being carried on a relay mobile, or outsidebroadcast van 51 (52) for marathon as shown in FIG. 53, a receivingantenna 50 of the receiving station or relay station is required to bealways directed toward the transmission antenna of the moving van bydirection adjustment so that strong radio waves can be received from thetransmission antenna. This direction adjusting operation for thereceiving antenna will hereinafter be simply called alignment.

To make the alignment easy, the conventional system shown in FIG. 17 isequipped with means for generating a low frequency signal in response tothe electric filed strength (S_(a) value) that is represented by thecontrol signal S_(a) in the AGC 9A (for example, means for generatingsound of tone interval proportional to the electric field strengththough not shown), and with a field strength level meter.

In the conventional analog signal transmission, the transmitted picturequality generally becomes better as the field strength is increased, andthus the operator only adjusts the antenna direction in order that thelevel meter can indicate the maximum value. In the digital transmission,however, the situation of relatively weak electric field strength, andno reflected wave, or presence of only the main wave will overwhelminglyoften provide satisfactory transmission condition as compared with thecondition of high electric field intensity and much reflected wavemixed.

FIG. 54 shows one example of the relation among the electric fieldstrength, error rate and reflected wave in the OFDM signal transmission.In this example, it is assumed that the guard interval period of OFDMsignal is selected to be 3 μs, and that a constant level reflected waveis mixed in the received signal. The abscissa, delay in FIG. 54 is delaytime between main wave and reflected wave. If the error rate as one ofthe evaluation parameter of signal transmission quality is 1.00E-02 orbelow, a video signal of moving pictures with allowable quality can betransmitted. As the error rate increases (in the upward direction alongthe ordinate of the graph of FIG. 54), the signal transmission qualitybecomes poor. From FIG. 54, it will be understood that the signaltransmission quality is, though affected by the electric field level, orthe CN or noise of the received signal, most affected by the reflectedwave (delayed wave). As illustrated in FIG. 54, when the filed strengthis reduced to −70 dBm or below, the noise component is graduallyincreased, or the error rate is deteriorated so that the error mixturerate in the signal is increased. In addition, when the delay time ofreflected wave exceeds the guard interval, or 3 μs, the error rategreatly increases. In FIG. 54, although the reflected wave level isassumed to be constant, the increase of the reflected wave level willincrease the error rate. Therefore, even if the filed strength isslightly lowered, the receiving antenna should be adjusted in itsorientation so that the reflected wave can be decreased or that thedelay time of reflected wave is confined within 3 μs.

Thus, it is difficult to achieve the best receiving condition in digitaltransmission by adjusting the antenna orientation while monitoring onlythe field intensity as in the prior art. It is necessary to adjust theantenna by considering the reflected wave in addition to the fieldstrength.

SUMMARY OF THE INVENTION

The present invention is to propose a system and method capable ofoffering the operator the means to display images by correctly imagingthe signal transmission status information that indicates at least thecondition of reflected waves in order to achieve the best receivingcondition on the receiving side when a digital signal is transmitted.

Since the conventional analog transmission system is greatly affected byreflected waves, it is used only under the condition that thetransmitting side and receiving side are placed under an unobstructedview. The recently developed digital transmission system of particularlyOFDM modulation system has less effect of reflected waves, and thus canbe positively used for beyond-the-horizon transmission as describedabove.

However, for beyond-the-horizon transmission, the antenna orientationadjustment operator cannot view the transmitting side. Therefore, inorder for the operator to make correct alignment relative to thetransmitting side that cannot be viewed, the operator needs to detectthe field strength and BER (Bit Error Rate), display them on anexclusive level meter or the like, and compare those with the reproducedpicture.

Here, in order to image the received signal in the digital transmissionsystem, it is necessary that the digital data D_(out) obtained by OFDMdemodulation in the above-mentioned receiving side processor 203 bedecoded by use of an MPEG decoder not shown. Thus, in the digitaltransmission system, since it is not easy to image the received signalon the receiving antenna side on which the antenna adjustment operatorengages in the adjustment, the alignment is often performed by use ofthe aforementioned exclusive field intensity or BER level meter.

However, since such situation as somewhat weak field strength and noreflected wave, or presence of only main wave in the digitaltransmission over-whelmingly often provides good transmission conditionas compared with the situation of strong field and presence of muchmixed reflected wave as described above, only comparing the fieldstrength and BER with the reproduced picture for the purpose ofalignment without grasping the situation in which the reflected wavesare mixed (ghost-status) does not always lead to high qualitytransmission.

The present invention is to remove these defects, and make it easy tomaintain high quality digital transmission by imaging the presence orabsence of reflected waves and the mixed state of reflected waves(ghost-status), imaging the field strength and BER value, and observingthese situations comprehensively for the alignment because thetransmission quality cannot always be perceived by measuring only thefield intensity and BER in the digital transmission of OFDM signal orthe like.

It is another object of the invention to display the imagedtransmission-condition in synchronism with other imaging signals, or inthe so-called superimposed state in order that the operator can makeantenna alignment with a plurality of outside broadcast vans withoutwatching a large number of monitors.

It is still another object of the invention to superimpose, when anabnormal transmission-condition is detected, the imaged abnormaltransmission-condition waveform on the normal transmission-conditionwaveform, and residually display those images for a predetermined time,thus making it possible to grasp the transmission path characteristics.

Moreover, it is an object of the invention to generate alarm sound whenthe abnormal state occurs in order to inform the operator of theabnormal state occurrence.

In addition, as shown in FIG. 53, a relay point 53 is provided on a hillor the hights in the general mobile relay, and digital imaging signalsare transmitted from the outside broadcast vans 51, 52 to the relaypoint 53 by use of the aforementioned OFDM transmission system. Theimaging signals received by the relay apparatus 53 provided on the hillare transmitted to a broadcast station 54 having studios via a microwavechannel 55 of analog transmission system.

A responsible person (a director) in this transmission system generallyworks on the studio side at the final receiving stage. He commands allthe transmission relay operations and orders workers at each place ofduty. For example, he orders to select and decide any ones to go on theair, from the images that have been transmitted from a plurality of vans51, 52.

In this case, although the mobile relay transmission-condition in thedigital transmission system changes every second as described above,even seeing only the video images transmitted without grasping theelectric field intensity, BER and the mixed state of reflected waves(ghost-status) cannot lead to correct decision of whether thetransmission-condition is good. The reason for this is that in thedigital transmission system the video images transmitted can besatisfactorily reproduced until the limited poor transmission conditionsin which the demodulation can be barely performed occur, and when thedemodulation cannot be made, an abnormal phenomenon such as freeze of areproduced picture on a display is suddenly caused.

Therefore, the director on the studio side cannot select appropriateon-air images from the video images transmitted from a plurality ofoutside broadcast vans because the transmission-condition of each van,or the field strength, BER and the mixed state of reflected waves(ghost-status) are uncertain. Thus, the selected on-air video images aresometimes suddenly frozen by a poor transmission-condition, leading to abroadcasting accident.

The present invention is to remove these defects, and make it possiblefor the director to correctly grasp the transmission-conditions bytransmitting information of the field strength, BER, and the mixed stateof reflected waves (ghost-status) that indicate thetransmission-conditions of these mobile relaying bodies from the OFDMtransmission system to a remote studio located distant therefrom, and bydisplaying those images.

According to one aspect of the invention, there is provided a digitalsignal transmission system using a digital modulation system comprisinga digital signal transmitter having a first digital signal processingunit and a digital signal receiver receiving a digital signal from thetransmitter. The digital signal receiver comprises a second digitalsignal processing unit for processing the digital signal from thetransmitter and outputting a digital demodulated signal and acorrelation value signal, a signal converter coupled with the seconddigital signal processing unit and supplied the correlation value signaltherefrom for generating a waveform indicating a transmission conditionincluding a main wave in response to the correlation value signal, and adisplay coupled with the signal converter for displaying the waveformindicating a transmission condition in the digital transmission system.

According to another aspect of the invention, there is provided adigital signal receiver to which a digital signal from a digital signaltransmitter using a digital modulation system is supplied. The digitalreceiver comprises a second digital signal processing unit forprocessing the digital signal and outputting a digital demodulatedsignal and a correlation value signal, a signal converter coupled withthe second digital signal processing unit and supplied said correlationvalue signal therefrom for generating a waveform indicating atransmission condition including a main wave and a reflected wave inresponse to the correlation value signal, and a display coupled with thesignal converter for digital signal.

According to still another aspect of the invention, there is provided amethod of displaying a digital signal transmission condition in adigital signal receiver. A digital signal is transmitted to the receiverfrom a digital signal transmitter using a digital modulation system. Themethod comprises the steps of processing the digital signal in a seconddigital signal processing unit of the digital signal receiver,outputting a digital demodulated signal and a correlation value signalfrom the second digital signal processing unit, generating a waveformindicating a transmission condition including a main wave in response tothe correlation value signal in a signal converter coupled with thesecond digital signal processing unit, and displaying the waveformindicating a transmission condition of the digital signal on a display.

According to further aspect of the invention, there is provided adigital signal transmission system by which a video signal modulated bya digital modulation system is transmitted via at least one relayapparatus to another receiver. In this digital signal transmissionsystem, the relay apparatus has a transmission condition signalgenerator for generating a ghost-status signal that indicates the mixedstate of reflected waves in the received video signal, a signalconverter for converting the ghost-status signal into a ghost-statusimaging signal so that the ghost-status signal can be imaged on adisplay, and a transmitter for transmitting the ghost-status imagingsignal and the video signal to the receiver. The receiver has circuitmeans for extracting the ghost-status imaging signal from the receivedsignal.

According to the invention, when at least ghost-status imaging signal oradditionally the BER imaging signal and field intensity imaging signalare displayed together on a video monitor, the transmission-conditionsbased on those imaging signals can be comprehensively viewed inassociation with each other, and thus be correctly grasped. Therefore,the antenna alignment operator can work for alignment effectively byviewing these images.

Moreover, according to the invention, the information of field strength,BER, and mixed state of reflected waves (ghost-status) that indicate theconditions of the signal transmission from the mobile relaying stationsis transmitted from the OFDM transmission system to a remote place, or astudio as the final receiving stage, where the transmission-conditionscan be displayed, and thus the director or other persons can correctlygrasp the transmission-conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the whole construction of oneembodiment of a digital transmission system according to the invention.

FIG. 2A is a block diagram of one example of thetransmission-condition-to-image converter 7 according to the invention.

FIG. 2B is a schematic diagram showing one example of the displayedstate of each transmission condition imaging signal on a display screen.

FIG. 3A is a block diagram of one example of thefield-intensity-to-image converter 7-1 according to the invention.

FIG. 3B is a schematic diagram showing one example of the displayedstate of the field strength imaging signal on a display screen.

FIG. 4A is a block diagram of one example of the BER-to-image converter7-2.

FIG. 4B is a schematic diagram showing one example of the displayedstate of the BER imaging signal on a display screen.

FIG. 5 is a block diagram showing the construction of one embodiment ofthe ghost-status-to-image converter 7-3 according to the invention.

FIG. 6 is a timing chart showing waveforms in the ghost-status-to-imageconverter 7-3 according to the invention.

FIG. 7 is a schematic diagram showing one example of the displayed stateof the ghost-status imaging signal according to the invention.

FIG. 8 is a block diagram showing the construction of one embodiment ofthe image integrator 7-4 according to the invention.

FIG. 9A is a schematic diagram showing one example of the displayedstate of the time scale and guard interval of the ghost-status imagingsignal.

FIG. 9B is a timing chart of the signal occurrence of synchronizingsignal, scale signal and interval signal.

FIGS. 10A through 10E are schematic diagrams showing examples of thetransmission-conditions displayed according to the invention.

FIG. 11 is a block diagram showing the construction of one embodiment ofa transmission-condition image superimposing device 7 b according to theinvention.

FIG. 12 is a block diagram showing the construction of one embodiment ofthe image integrator 7 b-4 according to the invention.

FIG. 13 is a block diagram showing the construction of one embodiment ofthe synchronizing signal generator 7 b-4-5 according to the invention.

FIG. 14 is a block diagram showing the construction of one embodiment ofthe BER-to-image converter 7 b-2 according to the invention.

FIG. 15 is a schematic diagram showing one example of the displayedstate of the BER imaging signal according to the invention.

FIG. 16 is a block diagram showing the whole construction of anotherembodiment of a video/audio transmission system according to theinvention.

FIG. 17 is a block diagram showing the whole construction of the generalOFDM transmission system.

FIG. 18 is a block diagram showing the construction of the synchronizingsymbol inserter 5 of the transmission system of FIG. 17.

FIG. 19 is a block diagram showing the construction of the synchronizingdetector & correlator 4A of the transmission system of FIG. 17.

FIG. 20 is a block diagram showing the construction of the NULL enddetector 4-1 of the synchronizing detector & correlator 4A of FIG. 19.

FIG. 21 is a timing chart to which reference is made in explaining theoperation for the NULL detection and SWEEP start position estimation.

FIGS. 22A, 22B and 22C are graphs showing examples of the correlationoutput signal S_(c) with no reflected wave.

FIG. 23 is a timing chart to which reference is made in explaining theoperation for the NULL detection and SWEEP start position estimation.

FIG. 24 is a graph showing one example of the correlation output signalS_(c) with reflected waves mixed.

FIG. 25 is a timing chart to which reference is made in explaining theoperation for the NULL detection and SWEEP start position estimation.

FIG. 26 is a graph showing one example of the correlation output signalS_(c) at a low field strength.

FIG. 27 is a block diagram showing one embodiment of aghost-status-to-image converter 7 a-3 according to the invention.

FIG. 28 is a schematic diagram showing one example of the displayedstate of each transmission-condition imaging signal according to theinvention.

FIG. 29 is a timing chart showing waveforms in the ghost-status-to-imageconverter 7 a-3 of FIG. 27.

FIG. 30 is a block diagram showing one example of thetransmission-condition-to-image converter 7 a according to theinvention.

FIG. 31 is a schematic diagram showing one example of the displayedstate of each transmission-condition imaging signal according to theinvention.

FIG. 32 is a block diagram showing one example of the abnormal-statedetector & residual display 7 a-5 according to the invention.

FIG. 33 is a block diagram showing one example of the abnormalghost-status residual display 7 a-5B according to the invention.

FIG. 34 is a schematic diagram to which reference is made in explainingthe divisional processing of the abnormal state detected screenaccording to the invention.

FIG. 35 is a block diagram showing one example of the abnormal statedetector 7 a-5A of the abnormal state detector & residual display 7 a-5FIG. 32.

FIG. 36 is a block diagram showing one example of the abnormalitydetection signal generator 7 a-5A-3 of the detector of the abnormalstate detector 7 a-5A of FIG. 35.

FIG. 37 is a block diagram showing one example of the abnormal conditiondetector 5A-3-3 according to the invention.

FIG. 38 is a block diagram showing one example of the FIFO writecontroller 7 a-5-13 of the abnormal ghost-status residual display 7 a-5Bof FIG. 33.

FIG. 39 is a timing chart showing waveforms in the abnormal statedetector & residual display 7 a-5 of FIG. 32.

FIG. 40 is a timing chart showing the operation of the abnormal statedetector 7 a-5A of FIG. 35.

FIG. 41 is a block diagram showing one example of atransmission-condition-to-image converter 7 a′ according to theinvention.

FIG. 42 is a block diagram showing one example of theghost-status-to-video state/abnormal-state detector & residual display 7a-7 according to the invention.

FIG. 43 is a block diagram showing one example of atransmission-condition-to-image converter 7 c according to theinvention.

FIGS. 44A and 44B are schematic diagrams showing examples of thedisplayed state of each transmission-condition imaging signal accordingto the invention.

FIG. 45 is a block diagram showing one example of the guard intervalmode detector 7 c-8 of the converter 7 c of FIG. 43.

FIGS. 46A and 46B are diagrams to which reference is made in explainingthe guard interval mode detection operation according to the invention.

FIG. 47 is a block diagram showing one example of theghost-status-to-image converter 7 c-3 according to the invention.

FIG. 48 is a block diagram of the counter 7 c-3-9 of theghost-status-to-image converter 7 c-3 of FIG. 47.

FIGS. 49A and 49B are waveform diagrams to which reference is made inexplaining the operation of the counter 7 c-3-9 of FIG. 48.

FIG. 50 is a block diagram showing one example of the image integrator 7c-4 according to the invention.

FIG. 51 is a block diagram showing one example of the external videosynchronizing type synchronizing signal generator 7 c-4-5 according tothe invention.

FIGS. 52A and 52B are schematic diagrams to which reference is made inexplaining the displayed states of the guard interval range.

FIG. 53 is a schematic diagram showing an example of the operation ofthe digital transmission system.

FIG. 54 is a diagram showing the relation among the field intensity,error rate and delay time between main wave and reflected wave.

FIG. 55 is a block diagram of the whole construction of anotherembodiment of a transmission system according to the invention.

FIGS. 56A, 56B and 56C are schematic diagrams showing the relationsbetween transmission signal wave-forms and displayed screens accordingto the invention.

FIG. 57 is a block diagram of one embodiment of the image integrator 7-4according to the invention.

FIG. 58 is a schematic diagram showing a transmission-conditionsuperimposed video signal wave-form according to the invention.

FIG. 59A is a block diagram of the field-intensity-to-image converter7-1 according to the invention.

FIG. 59B is a schematic diagram showing one example of the displayedpicture.

FIG. 60A is a block diagram of the BER-to-image converter 7-2 accordingto the invention.

FIG. 60B is a schematic diagram showing one example of the displayedpicture.

FIG. 61 is a block diagram showing the construction of theghost-status-to-image converter 7-3 according to the invention.

FIG. 62 is a timing chart of the signal at each part of theghost-status-to-image converter 7-3 according to the invention.

FIG. 63A is a block diagram of a superimposed information extractor &transmission-condition-to-image converter 7R according to the invention.

FIG. 63B is a schematic diagram showing one example of the displayedpicture.

FIG. 64A is a block diagram of a superimposed field intensity extractor& field-intensity-to-image converter 7-1V according to the invention.

FIG. 64B is a schematic diagram of one example of the displayed picture.

FIG. 65A is a block diagram of a superimposed BER extractor &BER-to-image converter 7-2V according to the invention.

FIG. 65B is a schematic diagram showing one example of the displayedpicture.

FIG. 66A is a block diagram of a superimposed ghost-status extractor &ghost-to-image converter 7-3V according to the invention.

FIG. 66B is a schematic diagram showing one example of the displayedpicture.

FIG. 67 is a timing chart to which reference is made in explaining theoperation of the superimposed ghost-status extractor & ghost-to-imageconverter 7-3V of FIG. 66A.

FIG. 68 is a block diagram showing the construction of one example of atransmission-condition image superimposing device andtransmission-condition adder according to the invention.

FIG. 69 is a schematic diagram showing one example of atransmission-condition superimposed imaging signal waveform according tothe invention.

FIG. 70A is a block diagram of a field-intensity-to-level converter 7-6according to the invention.

FIG. 70B is a schematic diagram showing one example of the displayedpicture.

FIG. 71A is a block diagram of a BER-to-level converter 7-7 according tothe invention.

FIG. 71B is a schematic diagram showing one example of the displayedpicture.

FIG. 72A is a block diagram of a time-to-BER converter 7-2Vr accordingto the invention.

FIG. 72B is a timing chart of signals in the time-to-BER converter7-2Vr.

FIG. 73 is a block diagram showing the whole construction of asingle-carrier system transmission system of still another embodiment ofthe invention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows the whole construction of an OFDM modulation typetransmission system according to the invention. The construction andoperation of chiefly the receiving side will be described.

This transmission system has the transmission-side processor 101 on thetransmitting side Tx as shown in detail in FIG. 17, the receiving-sideprocessor 203 on the receiving side Rx as shown in detail in FIG. 17, atransmission-condition-to-image converter 7, and a video display 11 asshown in FIG. 1.

Referring to FIG. 1, on the receiving side Rx, the AGC control signal Saindicating an electric field intensity that is produced from thereceiving-side processor 203, the correlation output Sc such as acorrelation value signal and the signal Sb indicating BER are suppliedto the transmission-condition-to-image converter 7. Also, the pulseFSTrc as the operation timing reference from the receiving-sideprocessor 203 is supplied to the transmission-condition-to-imageconverter 7. The transmission-condition imaging signal thus generatedfrom the converter 7 is displayed on the video display 11.

FIG. 2A is a block diagram of one embodiment of thetransmission-condition-to-image converter 7. With reference to FIG. 2A,this converter will be described.

The control signal Sa is supplied to the input end of thefield-intensity-to-image converter 7-1. The output from thefield-intensity-to-image converter 7-1 is fed to the input end of theimage integrator 7-4.

The signal Sb is supplied to the input end of the BER-to-image converter7-2. The output from the BER-to-image converter 7-2 is fed to the imageintegrator 7-4.

The signal Sc and signal FSTrc are supplied to the input ends of theghost-status-to-image converter 7-3. The output from theghost-status-to-image converter 7-3 is fed to the image integrator 7-4.

The synchronizing signal C.Sync from the image integrator 7-4 issupplied to the synchronizing input ends of the field-intensity-to-imageconverter 7-1, BER-to-image converter 7-2 and ghost-status-to-imageconverter 7-3. The image integrator 7-4 produces atransmission-condition imaging signal which will be described later.

The field-intensity-to-image converter 7-1, BER-to-image converter 7-2and ghost-status-to-image converter 7-3 are responsive to thesynchronizing signal C.Sync to convert their input condition, or statussignals to imaging signals. The image integrator 7-4 combines theseimaging signals to form a transmission-condition imaging signal with avideo synchronizing signal added.

FIG. 2B shows one example of the displayed picture, or screen of eachtransmission-condition imaging signal. This example will be describedbelow.

The ghost-status image is displayed as a correlation output waveform ofa bar graph or sequential line graph with a time scale and guardinterval range added on the left side of the screen. Here, a high peakdue to main wave and a low peak due to reflected wave are shown. The BERimage is displayed as dot blocks of intermediate size on the upper rightside of the screen. The field strength image is displayed as a fewcolumns of stacked small blocks arranged on the lower right side of thescreen. These waveforms and block number are changed in accordance withthe transmission conditions. These transmission condition images areupdated depending on the renewal period of the imaging signals receivedand decoded.

FIG. 3A is a block diagram of one embodiment of thefield-intensity-to-image converter 7-1. FIG. 3B is a schematic diagramshowing the displayed state of the field-strength image. This converterwill be described with reference to those figures.

The control signal Sa indicative of a field strength is supplied to andconverted by an A/D converter 7-1-1 into a digital signal DSa of, forexample, 6 bits. The signal DSa indicative of a field strength ischanged to, for example, a 24-bit binary signal of Da0-Da23 by a decoder(DEC) 7-1-2. Here, if signal DSa is 01 h, or 1 in decimal notation, onlyDa0 and Da1 become level “High”. If signal DSa is 15 h, or 21 in decimalnotation, Da0 through Da21 become level “High”.

These bits Da0 through Da23 are respectively supplied to 24 AND gates(AND) 7-1-4. The 24 outputs from the AND 7-1-4 are supplied to an ORgate (OR) 7-1-5. The synchronizing signal C.Sync is supplied to adisplay position pulse generator 7-1-3, which then generates displayposition pulses a0 through a23 in synchronism with the synchronizingsignal C.Sync. These pulses a0 through a23 are supplied to the otherinput ends of the AND 7-1-4, which then computes the logical products ofthese pulses and signals Da0 through Da23, respectively.

Here, if the signal DSa indicative of a field strength is 00 h, or zeroin decimal notation, only the signal Da0 becomes level “High”. Thus,only the logical product of pulse a0 and signal Da0 is “High”, only theblock at the position corresponding to pulse a0 is displayed. If signalDSa is 16 h, or 22 in decimal notation, the products of signals Da0through Da22 and pulses a0 through a22 are “High”. Thus, all the blocksat the positions corresponding to pulses a0 through a22 are displayed.

Here, if it is assumed that the pulse a0 becomes level “High” at theposition of scanning lines 208-th H (Horizontal line) through 210-th H,and sample numbers 384-th through 414-th sample, the pulse a22 is level“High” at the position of scanning lines 202-th H through 204-th H, andsample numbers 540-th through 570-th sample, and pulse a23 is level“High” at the position of scanning lines 199-th H through 201-st H, andsample numbers 540-th through 570-th sample, then the field strengthimage will be displayed as shown in FIG. 3B.

In other words, the number of blocks corresponding to the field strengthimage is changed in accordance with the value of the control signal Saindicative of a field strength.

FIG. 4A is a block diagram of one embodiment of the BER-to-imageconverter 7-2. FIG. 4B is a schematic diagram showing the displayedstate of the BER condition imaging signal on the display. This converterwill be described.

The signal Sb indicative of a BER condition is supplied to and convertedby an A/D converter 7-2-1 into a digital signal DSb of about 3 bits. Thesignal DSb indicative of the BER condition is converted by a decoder(DEC) 7-2-2 to, for example, all five signals of Db0 through Db4.

Here, if the signal DSb is 01 h, or one in decimal notation, onlysignals Db1 and Db0 become level “High”. The outputs of Db0 through Db4are supplied to five AND gates (AND) 7-2-4. The five outputs from theAND 7-2-4 are supplied to an OR gate (OR) 7-2-5.

The synchronizing signal C.Sync is supplied to a display position pulsegenerator 7-2-3, which then produces pulses b0 through b4 for the BERcondition in synchronism with the synchronizing signal C.Sync. Thepulses b0 through b4 for the BER condition are displayed on the displayas shown in FIG. 4B.

The pulses b0 through b4 are supplied to the other input terminals ofthe AND 7-2-4, which compute the logical products of those pulses andthe signals Db0 through Db4, respectively. Here, if the signal DSbindicative of BER is 00 h, or 0 in decimal notation, only the signal Db0is level “High”. Thus, the product of the pulse b0 and signal Db0becomes level “High”, and only the block at the position correspondingto pulse b0 is displayed. If the signal DSb is 03 h, or 3 in decimalnotation, the logical products of signals Db0 through Db3 and pulses b0through b3 are level “High”. Thus, all blocks at the positionscorresponding to pulses b0 through b3 are displayed.

In other words, the block number of the BER image is changed dependingon the value of the control signal Sb indicative of the BER condition.

A description will be made of the logical processing for displaying theBER condition displaying pulses b0 through b4 on the display as shown inFIG. 4B.

The display position pulse generator 7-2-3, if it is used for NTSC,makes logical operation using a 1/910 frequency dividing counter thatcounts at a clock of 14.3 MHz and is reset with a horizontal scanningperiod and a 1/525 frequency dividing counter that counts at a clock ofa half horizontal scanning period and is reset with a vertical scanningperiod.

Thus, as shown in FIG. 4B, the b4 pulse, for instance, is displayed atthe position of scanning lines of 80-th H through 96-th H, and samplenumber of 512-nd through 526-th sample, and the b3 pulse-at the positionof scanning lines of 80-th H through 96-th H, and sample number of528-th through 542-nd sample. The b2 pulse is displayed at the positionof scanning lines of 80-th H through 96-th H, and sample number of544-th through 558-th sample. The b1 pulse is displayed at the positionof scanning lines of 80-th H through 96-th H, and sample number of560-th through 574-th sample. The b0 pulse is displayed at the positionof scanning lines of 80-th H through 96-th H, and sample number of576-th through 590-th sample.

FIG. 5 is a block diagram of one embodiment of the ghost-status-to-imageconverter 7-3. This example will be described.

The correlation output signal Sc indicative of the ghost-status issupplied to and converted by an A/D converter 7-3-1 to a digitalcorrelation output signal DSc of 8 bits. This signal DSc is supplied toan input of a FIFO 7-3-2. The pulse FSTrc with frame period is suppliedto the write-in reset terminal of the FIFO 7-3-2. The digitalcorrelation output signal D′Sc from the FIFO 7-3-2 is supplied to acomparator 7-3-4. The output from the comparator 7-3-4, or a ghost levelsignal LE is supplied to a gate 7-3-6. The synchronizing signal C.Syncis supplied to a timing pulse generator 7-3-3. The generator 7-3-3 isresponsive to the synchronizing signal C.Sync to supply a read resetsignal RRST and read enable signal RE to the FIFO 7-3-2, a synchronizingsignal HD to an H-counter 7-3-5, and a blanking gate signal BG to thegate 7-3-6. The H-counter 7-3-5 generates a triangular-wave signal Dh ofH (Horizontal scanning) period in response to the signal HD, andsupplies it to the comparator 7-3-4.

FIG. 6 is a timing chart showing the relation among the signals C.Sync,RRST, RE, HD, Dh, BG and LE. The operation of this converter will bedescribed with reference to FIGS. 5 and 6.

The timing pulse generator 7-3-3 generates the reset signal RRST at thestart of each video field period, and forces the FIFO (first-infirst-out memory) 7-3-2 to make it ready to read from the firstwritten-in content. In addition, it generates the RE signal at each Hperiod, and orders the FIFO 7-3-2 to sequentially read the written-incontents (DSc) one by one. The signal D′Sc read at each video H-periodis supplied to the comparator 7-3-4 where it is compared with the valueDh of each H-period. Thus, the comparator produces the ghost levelsignal LE that becomes level “High” when D′Sc is larger than Dh, orD′Sc>Dh. Here, in order to prevent the signal LE from being generated inthe blanking periods, the signal BG that becomes level “Low” in theblanking periods is generated, making the ghost level signal LE forciblylevel “Low”.

Therefore, if the correlation output signal Sc has high level, the gate7-3-6 produces the signal LE of a long High-level period as theghost-status imaging signal, or ghost imaging signal.

A description will be made of the case in which the ghost imaging signalis displayed by a bar graph on the left side of the display screen inthe vertical direction along the time base as shown in FIG. 7. Here, itis assumed that the ghost level signal LE corresponding to the n-thscanning line is the main wave, and takes the maximum. It is alsoassumed thaat the signal Dh is incremented by one at each two samples,and finally reaches about 450.

If the signal D′Sc corresponding to the n-th scanning line is a value of241, the time at which the value of Dh from the H-counter 7-3-5 exceeds241 is at the 482-nd sample, and thus the ghost level signal LE will belevel “High” during the time interval of the first sample through 482-ndsample. However, since the signal BG is L level during the interval fromthe first sample to 90-th sample, the signal LE gated is level “Low”when the signal BG is level “Low”. Thus, the ghost imaging signalcorresponding to the n-th scanning line become level “High” during theinterval from 91-st sample to 482-nd sample, with the result that the LEof the n-th scanning line can be displayed as shown in FIG. 7.

If the signal D′Sc corresponding to the (n+1)-th scanning line is avalue of 123, the time at which the value of Dh exceeds 123 is at the246-th sample. The LE will be level “High” during the interval from thefirst sample to the 246-th sample. However, since the signal BG of Llevel is supplied to the gate as mentioned above, the ghost imagingsignal corresponding to the (n+1)-th scanning line becomes level “High”during the interval from the 91-st to the 246-th sample, so that the LEof the (n+1)-th scanning line is displayed as shown in FIG. 7.

Similarly, if the signal D′Sc corresponding to the (n−2)-th scanningline is a value of 89, the time at which the value of Dh exceeds 89 isat the 178-th sample, and thus the ghost level signal LE will be level“High” during the interval from the first sample to the 178-th sample.However, since the signal BG of L level is supplied to the gate asabove, the ghost imaging signal of the (n−2)-th scanning line becomeslevel “High” during the interval from the 91-st to 178-th sample, andthus displayed as shown in FIG. 7.

FIG. 8 is a block diagram of one embodiment of the image integrator 7-4.This integrator will be described.

The field-intensity imaging signal, BER imaging signal and ghost imagingsignal are supplied to an adder 7-4-6 via gates 7-4-1, 7-4-2, 7-4-3,respectively.

A display selector 7-4-4 generates signals for individually selecting(ON/OFF) one being displayed, of the field-intensity imaging signal, BERimaging signal and ghost imaging signal. A video synchronizing signalgenerator 7-4-5 supplies the synchronizing signal C.Sync to the adder7-4-6 and the outside, and a pulse indicative of the time base scale andguard interval for the ghost imaging signal to the adder 7-4-6. If thevideo synchronizing signal generator 7-4-5 is used for NTSC, it makeslogic processing by use of a 1/910 frequency dividing counter thatcounts at a clock of 14.3 MHz and is reset with H-period, and by a 1/525frequency dividing counter that counts at a clock of 1/2 H (Horizontalperiod) and is reset with V (Vertical)-period. The gates 7-4-1, 7-4-2,7-4-3 respectively respond to the signals from the display selector7-4-4 to allow the field-intensity imaging signal, BER imaging signaland ghost imaging signal to pass therethrough or not. The adder 7-4-6adds each imaging signal that has passed through the gate 7-4-1, 7-4-2,7-4-3, and the signal indicative of the scale and interval insynchronism with the synchronizing signal C.Sync to produce atransmission-condition imaging signal in order that each imaging signalcan be displayed as blocks, dots or bar graph of a certain size on thedisplay screen at a predetermined position.

One example of the rates of the imaging signals to be added in the adder7-4-6 will be given below. If all signals fed to the adder 7-4-6 have +5V in digital level, the rates of the field-intensity imaging signal, BERimaging signal and ghost imaging signal are 0.2, the rates of the scalesignal and interval signal are 0.05, and the rate of the synchronizingsignal C.Sync is 0.1. Thus, the transmission-condition imaging signalgenerated has about 1 Volt_(p-p) including the synchronizing signal.

FIG. 9A is a schematic diagram showing a signal cur of time base scaleand a signal C-GI of guard interval for the ghost imaging signal on themonitor screen. FIG. 9B is a timing chart showing the generation of thescale signal cur and interval signal C-GI with respect to thesynchronizing signal C.Sync.

It is assumed that the time scale signal cur becomes level “High” atintervals of 16 Hs in the range from the 32-nd H to the 240-th H and atlateral positions from the 108-th to 144-th sample within the effectiverange of the monitor. It is also assumed that the interval signal C-GIbecomes level “High” at scanning lines from the 112-nd H to 160-th H,and in the sample range from the 112-nd to 128-th sample.

The signal C-GI indicative of the guard interval, when the transmissioncondition is normal, is set to start being displayed from the n-thscanning line at which the main wave should exist, and to end 48 Hsafter when the guard interval is 3 μsec and the sampling clock frequencyfor OFDM is 16 MHz. Thus, it becomes a band shape image indicating 3μsec. The signal cur indicative of the time scale, if the sample clockfrequency for OFDM is 16 MHz, provides a scale at intervals of 1 μsec bysetting it to be level “High” at intervals of 16 Hs.

FIGS. 10A to 10E are schematic diagrams showing differenttransmission-condition displaying screens. With reference to thesefigures, a description will be made of the situation in which theoperator can correctly grasp the present transmission-condition bydisplaying the ghost imaging signal, BER imaging signal and fieldintensity imaging signal on the monitor.

FIG. 10A shows one example of the ghost image displayed when the mainwave of high level with no reflected wave is received. In this case, ahigh-level peak indicating the main wave is present at around the n-thscanning line within a guard interval of 2 μsec indicated by a dottedline. In addition, the BER condition displayed on the upper right sideand the field intensity displayed on the lower right side aresatisfactory values. Thus, it will be seen that this screen shows a verygood transmission-condition.

FIG. 10B shows one example of the ghost image displayed when the mainwave of high level is received and a reflected wave of intermediatelevel is received within the guard interval (2 μsec) after the receptionof the main wave. In this case, the high-level main wave exists ataround the n-th scanning line within the guard interval, and the secondpeak of intermediate level is displayed at about ⅔ of the guardinterval. From this screen, it will be understood that the reflectedwave of intermediate level exists as the second peak and is within adelay time of about 2 μsec, or within the guard interval so as to beneglected. In addition, the BER condition and field strength arerelatively good. Consequently, this screen shows a satisfactorytransmission-condition.

FIG. 10C shows one example of the ghost image displayed when the mainwave of high level is received and a reflected wave of low level isreceived 5 μsec after the reception of the main wave, or beyond theguard interval. In this case, a high peak of the high-level main waveexists at around the n-th scanning line within the guard interval, and asecond low peak appears beyond the guard interval. From this figure, itwill be understood that, since a reflected wave of a low level peakoccurs about 5 μsec after the main wave, or beyond the guard interval,the effect of the reflected wave cannot be compensated by the guardinterval. In addition, the field intensity is good, but the BER issomewhat poor. Thus, this screen shows a slightly unsatisfactorytransmission condition. In this case, the operator might adjust theantenna orientation so that the delay time of the reflected wave can beconfined within the guard interval.

FIG. 10D shows one example of the ghost image displayed when the mainwave of intermediate level is received, and when a reflected wave ofhigh level occurs 5 μsec after the reception of the main wave, or beyondthe guard interval. In this case, a peak of the main wave exists ataround the n-th scanning line within the guard interval, and the secondpeak of high level appears out of the guard interval. From this figure,it will be understood that since the reflected wave of larger level thanthe main wave occurs about 5 μsec after the main wave, or beyond theguard interval, the reflected wave of high level cannot be neglected. Inaddition, the BER, and field intensity are both poor. Thus, this screenshows an unsatisfactory transmission-condition. In this case, theoperator would need to adjust the antenna orientation so that the levelof the main wave in the received signal can be increased.

FIG. 10E shows one example of the ghost image displayed when the mainwave of low level is received, and when a reflected wave of high levelarrives as short as 2 μsec after the reception of the main wave.

In this case, a low peak of the main wave exists before the n-thscanning line, and a second high peak appears at around the n-thscanning line within the guard interval. From the figure, it will beseen that not the main wave of the first low peak but the reflected waveof the second high peak is about to be received and synchronized with.In addition, the field intensity is satisfactory, but the BER is poor.Thus, this screen shows a considerably unsatisfactorytransmission-condition.

Since this reflected wave of high level is normally not kept high level,but will disappear before long, it is highly likely that phase shiftingof clock occurs to switch the synchronized reception back to the mainwave when the reflected wave level is reduced. In this case, there isthe possibility that the BER value becomes very poor, and it can bepredicted that a very poor transmission-condition occurs in a shorttime. Therefore, this received signal might not be used for videobroadcasting. A signal received from other outside broadcast vans mightbe used.

Thus, by displaying the ghost imaging signal, BER imaging signal andfield intensity imaging signal on the monitor display, it is possible tocorrectly grasp the transmission-condition because the conditions ofthese imaging signals can be comprehensively observed in associationwith each other.

Therefore, the operator to adjust the antenna orientation is able toeffectively make alignment operation while viewing these displayedimages.

FIG. 11 is a block diagram of one embodiment of thetransmission-condition image superimposing device 7 b for superimposingthe transmission-condition imaging signals and the received and decodedvideo signal. This superimposing device 7 b can replace thetransmission-condition-to-image converter 7 shown in FIG. 1. Thissuperimposing device 7 b will be described below.

The digital data D_(out) produced from the receiving-side processor 203of FIG. 1 by OFDM demodulation is decoded by an MPEG decoder not showninto the video signal, which is then supplied to the image integrator 7b-4. The control signal Sa indicative of a field intensity, the signalSb indicative of BER, and the correlation output signal Sc are suppliedto a field-intensity-to-image converter 7 b-1, a BER-to-image converter7 b-2 and a ghost-to-image converter 7 b-3, respectively. The imagingsignals from those converters are supplied to the image integrator 7b-4.

FIG. 12 is a block diagram of this image integrator 7 b-4. Thisintegrator will be described.

The video signal resulting from the reception and decoding is suppliedto an external video synch type synchronizing signal generator 7 b-4-5and to an adder 7 b-4-6. The field intensity imaging signal, BER imagingsignal and ghost imaging signal are supplied via gates 7 b-4-1, 7 b-4-2,7 b-4-3 to the adder 7 b-4-6.

A display selector 7 b-4-4 generates signals for individually selecting(ON/OFF) ones being displayed, of the field intensity imaging signal,BER imaging signal and ghost imaging signal. The external video synchtype synchronizing signal generator 7 b-4-5 supplies the synchronizingsignal C.Sync resulting from extracting from the input video signal tothe adder 7 b-4-6 and to the outside, and also a pulse of the time basescale and guard interval for the ghost imaging signal to the adder 7b-4-6. The gates 7 b-4-1, 7 b-4-2, 7 b-4-3 respond to the selectionsignals from the display selector 7 b-4-4 to allow the field intensityimaging signal, BER imaging signal and ghost imaging signal to be passedtherethrough or not. The adder 7 b-4-6 responds to the C.Sync to add theimaging signals passed through the gates 7 b-4-1, 7 b-4-2, 7 b-4-3, thepulse signal of the scale and interval, and the video signal produced bythe reception and decoding to produce a transmission-conditionssuperimposed imaging signal so that each imaging signal can be displayedin a certain size at a position.

This transmission-conditions superimposed imaging signal is displayed ona monitor. Thus, since the operator can comprehensively view thereproduced images of those imaging signals in association with eachother, the transmission-conditions can be correctly grasped as comparedwith the case shown in FIG. 10.

One example of the addition rates of those signals in the adder 7 b-4-6will be given below.

If all the signals fed to the adder 7 b-4-6 are +5 V in digital level,the rates of the field intensity imaging signal, BER imaging signal andghost imaging signal are 0.2, the rates of the time scale signal andinterval signal are 0.05, and the rate of the analog video signal ofwhich the video portion is about 0.7 V is one.

FIG. 13 is a block diagram of one embodiment of the external video synchtype synchronizing signal generator 7 b-4-5. This generator will bedescribed.

In the external video synch type synchronizing signal generator 7 b-4-5,a synchronizing signal extractor 7 b-4-5-1 extracts the external synchsignal from the input video signal. In addition, a synch signalgenerator 7 b-4-5-2 produces the internal synch signal C.Sync insynchronism with the external synch signal.

The pulse of the above time base scale and guard interval is similarlyproduced as in the above image integrator 7-4.

FIG. 14 is a block diagram of one embodiment of the BER-to-imageconverter 7 b-2 of the display position switching type. The portionsdifferent from the BER-to-image converter 7-2 will be described.

A display position pulse generator 7 b-2-3 generates pulses b0 throughb4 for the indication of BER in synchronism with the sync signal C.Synclike the BER-to-image converter 7-2, but it also generates, by a modeswitching signal, pulses b′0 through b′4 corresponding to anotherposition. FIG. 15 schematically shows the situation in which the imagescan be displayed by switching at different positions corresponding tothese pulses b0 through b4, b′0 through b′4.

If the generator 7 b-2-3 is used for NTSC, it makes logical processingby use of a 1/910 frequency dividing counter that counts at a clock of14.3 MHz and is reset at each H-period, and a 1/525 frequency dividingcounter that counts at a clock of 1/2 H and is reset at each V-period.

Thus, in the case of using the mode switching signal=High (mode 1), theblocks are displayed at a position corresponding to the pulse b0 throughb4 on the upper right side. In the case of using the mode switchingsignal=Low (mode 2), the blocks are displayed at a positioncorresponding to the pulse b′0 through b′4 on the lower right side.

For example, as shown in FIG. 15, the b4 signal is displayed at aposition of scanning lines 80-th H through 96-th H, and of sample number512-nd through 526-th sample. The b3 signal is displayed at a positionof scanning lines 80-th H through 96-th H, and of sample number 528-ththrough 542-nd sample. The b2 signal is displayed at a position ofscanning lines 80-th H through 96-th H, and of sample number 544-ththrough 558-th sample. The b1 signal is displayed at a position ofscanning lines 80-th H through 96-th H, and of sample number 560-ththrough 574-th sample. The b0 signal is displayed at a position ofscanning lines 80-th H through 96-th H, and of sample number 576-ththrough 590-th sample.

In addition, the b′4 signal is displayed at a position of scanning lines192-nd H through 208-th H, and of sample number 520-th through 534-thsample. The following signals b′3, b′2 and b′1 are displayed atpositions in the same way. The signal b′0 is displayed at a position ofscanning lines 192-nd H through 208-th H, and of sample number 584-ththrough 598-th sample.

FIG. 16 is a block diagram of one embodiment of a video/audiotransmission system, having a combination of the transmission systemaccording to the invention and a video codec, by which theafore-mentioned transmission-condition images are superimposed on anMPEG decoded image before being displayed. Portions different from thetransmission system using OFDM modulation system shown in FIG. 1 will bedescribed.

On the transmission side, a video signal and an audio signal are fed toan MPEG-ENC (encoder) 101 M, where they are converted to compresseddigital data D_(in) in synchronism with the reference clock CK_(TX) fedfrom the transmission-side processor 101. On the receiving side, thetransmitted and received signal is demodulated by the receiving-sideprocessor 203. The demodulated output D_(out) is supplied to an MPEG-DEC(decoder) 203 M for expansion. The video signal expanded by the MPEG-DEC203 M is supplied to the transmission-condition video superimposingdevice 7 b that is the same as shown in FIG. 11, where it issuperimposed on each condition imaging signal, and the time scale andguard interval signal as shown in FIG. 2B to produce atransmission-condition superimposed video signal.

This transmission-condition superimposed video signal is displayed onthe video display 11. Thus, since each condition imaging signal and thereceived and decoded video signal can be comprehensively observed inassociation with each other, the operator is able to correctly grasp thetransmission conditions.

According to the invention, since the field intensity, BER and ghost areconverted to imaging signals, they can be displayed on a common type ofvideo display, and hence they can be displayed in optimum sizesaccording to situations, if necessary.

Moreover, if the ghost imaging signal within a certain level range isdisplayed in a different way (with a different luminance level or hue)from signals occurring within other level ranges, the operator is ableto quickly find the transmission condition that is to be noted.

In addition, if the guard interval of the ghost imaging signal isdisplayed in a different way (with a different luminance level or hue)to distinguish from other condition imaging signals, the operator canpromptly find the transmission condition that is to be looked out orconsidered.

Also, since the transmission-condition measured data are converted toimaging signals, they can be recorded on video cassette recorders orother recording media, and thus a large amount of transmission-conditiondata measured and collected can be recorded easily and at low cost.

Therefore, since the ghost imaging signal, BER imaging signal and fieldintensity imaging signal can be displayed on a video monitor, thevarious condition images can be comprehensively seen in association witheach other, and hence the operator can correctly understand thetransmission conditions.

Accordingly, the antenna alignment operator can effectively perform thealignment operation while viewing the imaged information on the screen.

Another embodiment of the ghost-to-image converter different from theghost-to-image converters 7-3, 7 b-3 (FIGS. 5 and 11) in thetransmission-condition-to-image converter 7 and transmission-conditionimage superimposing device 7 b (FIGS. 2A and 11) will be described withreference to FIGS. 27, 28 and 29.

Since the ghost-status imaging signal produced from the ghost-to-imageconverter 7-3 shown in FIG. 5 is vertically displayed as an image like abar graph on the left side of the screen as shown in FIG. 7, theresolution is limited by the number of scanning lines. Moreover, sincethe time base is displayed in the vertical direction, it is inconsistentwith the human sixth sense, so that in the alignment operation in whichthe operator needs swift decision, he additionally makes the mentaloperation to change the direction of time base in his mind though it isunconnected with the original operation.

Thus, in this embodiment, the ghost imaging signal indicative of a ghoststatus is displayed in the lateral direction with respect to the screenwith the display resolution or display range magnified, and the timebase is provided in the lateral direction. Consequently, the alignmentoperator can view the ghost status with the same feeling as he watchesthe oscilloscope screen.

FIG. 27 is a block diagram showing the construction of theghost-to-image converter 7 a-3 for lateral display according to theinvention. FIG. 28 is a schematic diagram showing the image-displayedscreen. FIG. 29 is a diagram showing the waveforms of signals.

The constructions of the other portions than the ghost-to-imageconverters 7-3, 7 b-3 of the transmission-condition-to-image converter 7and transmission-condition image superimposing device 7 b will not bedescribed because they are the same as in FIGS. 2, 5 and 11.

Referring to FIG. 27, the correlation output signal Sc indicative of theghost status is supplied to and converted by an A/D converter 7 a-3-1into the digital correlation output signal DSc of, for example, 8 bits.This signal DSc is supplied to an FIFO 7 a-3-2.

The pulse FSTrc of frame period is supplied to an input terminal of thewrite-in reset terminal of the FIFO 7 a-3-2. The digital correlationoutput signal D′Sch from the FIFO 7 a-3-2 is supplied to a comparator 7a-3-4. The output, or ghost level signal LEh from the comparator 7 a-3-4is supplied to a gate 7 a-3-5.

Moreover, the synchronizing signal C.Sync is supplied to a clock (CK)reproducer 7 a-3-6, an HD extractor 7 a-3-7 and a VD extractor 7 a-3-8.The clock produced from the CK reproducer 7 a-3-6 is supplied to acounter 7 a-3-9. The output WE from the counter 7 a-3-9 is supplied tothe WE terminal of the FIFO 7 a-3-2.

The output HD from the HD extractor 7 a-3-7 is supplied to a counter 7a-3-10. The output C-S from the counter 7 a-3-10 is supplied to a firstdecoder 7 a-3-3.

The output VD from the VD extractor 7 a-3-8 is supplied to an H-counter7 a-3-11. The output C-H from the H-counter 7 a-3-11 is supplied to thefirst decoder 7 a-3-3 and a second decoder 7 a-3-12.

The first decoder 7 a-3-3 supplies a read reset signal RRST to the RRterminal of the FIFO 7 a-3-2, and a read enable signal RE to the REterminal of the FIFO 7 a-3-2.

The output (D′Sch) from the FIFO 7 a-3-2 is supplied to an input of thecomparator 7 a-3-4. The output Dhh from the second decoder 7 a-3-12 issupplied to the other terminal of the comparator 7 a-3-4. The output LEhfrom the comparator 7 a-3-4 is supplied to the gate 7 a-3-5.

The CK reproducer 7 a-3-6 reproduces a clock (CK) of, for example, 14.3MHz from the synchronizing signal C.Sync. The counter 7 a-3-9 dividesthe frequency of the CK, and generates the WE signal with the perioddepending on that of the correlation output signal Sc. The HD extractor7 a-3-7 extracts the H-period component from the synchronizing signalC.Sync, and produces the HD signal with H-period. The counter 7 a-3-10is reset by the HD signal, and produces the counter signal C-S thatincreases at each CK period. The VD extractor 7 a-3-8 extracts theV-period component from the synchronizing signal C.Sync, and producesthe VD signal with V-period. The H-counter 7 a-3-11 is reset by the VDsignal, and produces the counter signal C-H that increases at eachH-period.

The decoder 7 a-3-3 receives the counter signals C-S, C-H and producesthe read reset signal RRST that takes level “Low” in 1 H period at eachCK period within the interval from the m-th scanning line to the(m+n)-th scanning line in each V-period as shown in FIG. 29. Thus, theread address to the FIFO 7 a-3-2 is initialized into address 0.

In addition, the read enable signal RE that takes level “High” duringeach interval from the m-th scanning line to the (m+n)-th scanning lineforces the read address to the FIFO 7 a-3-2 to proceed, with the resultthat the output D′Sch as the correlation output signal Sc is read fromthe FIFO 7 a-3-2.

The decoder 7 a-3-12 receives the counter signal C-H, and produces level1 a at the m-th scanning line as output Dhh, and then reduces the levelby i at each H. At the (m+n)-th scanning line, the decoder producesoutput Dhh of 1 a minus ni.

At this time, the comparator 7 a-3-4 compares the D′Sch as thecorrelation output Sc and the decoder output Dhh, and produces thesignal LEh that becomes level “High” when the condition of D′Sch>Dhh issatisfied.

In other words, as illustrated in FIG. 29, since the D′Sch is lower thanor equal to Dhh during all the m-th H, the signal LEh remains level“Low”. During the (m+1)-th H, the condition of D′Sch>Dhh is satisfiedonly in a short period, t₁ at the center of that H, and at this time thesignal LEh becomes level “High”. During the (m+2)-th H, since thecondition of D′Sch>Dhh is satisfied in a wider period, t₂ than theprevious short period t₁, the signal LEh takes level “High” for moretime. Thereafter, after these operations are repeated, the waveform ofthe correlation output signal Sc is expressed by such a scanning linestructure as shown in FIG. 29 at LEh.

Thus, the correlation output signal Sc indicative of the ghost statuscan be converted to an image, and as shown in FIG. 28, the ghost imagecan be laterally displayed with respect to the time base on the screen.

In FIG. 29, for simple explanation, only the main wave of thecorrelation output signal Sc indicative of the ghost status is expressedas the signal LEh in the form of scanning line structure.

Another embodiment of the converter than thetransmission-condition-to-image converter 7, and transmission-conditionimage superimposing device 7 b (FIGS. 2A and 11) will be described withreference to FIGS. 30 through 40.

When we try to grasp the transmission path conditions from the ghostimaging signal, BER imaging signal and field intensity imaging signal,the operator needs to always fix his eyes on the monitor screen againstabnormal state occurrence. This becomes a considerable burden on theoperator.

In addition, when an abnormal thing occurs suddenly for a very shorttime, the human cannot perceive it as an abnormal state through theeyes, or the operator cannot grasp correct transmission path conditions.

Thus, in this embodiment, when the apparatus detects that theinformation indicative of a ghost imaging signal or others has reached apredetermined unsatisfactory level because of poor transmissioncondition, it superimposes this abnormal transmission-condition waveformon the current normal transmission-condition waveform and keeps itresidually displayed as it is for a certain time so that the operatorcan understand the transmission path characteristics.

In addition, warning sound is emanated at the time of this abnormalstate, notifying the operator of the abnormal thing.

FIG. 30 is a block diagram of the construction of thetransmission-condition-to-image converter 7 a having the abnormalitydetection and residual displaying functions according to the invention.The transmission-condition-to-image converter 7 a is different from thetransmission-condition-to-image converter 7 and transmission-conditionimage super-imposing device 7 b in that an abnormal state detector &residual image display 7 a-5 and abnormal state image integrator 7 a-6are further added.

In this converter, it is not always necessary to simultaneously displaythe ghost imaging signal, or abnormal state image together with thefield intensity and BER imaging signals. This converter can beimplemented by hardware, DSP (Digital Signal Processor) or one-chipmicrocomputer.

Referring to FIG. 30, the correlation output signal Sc indicative of theghost status, and the pulse FSTrc with frame period are supplied to theabnormal state detector & residual image display 7 a-5.

The output S′c of the ghost-to-image converter 7 a-3 is connected to theabnormal state detector & residual image display 7 a-5. The output fromthe image integrator 7 a-4 and the output CNT from the abnormal statedetector & residual image display 7 a-5 are supplied to the abnormalstate image integrator 7 a-6.

The abnormal state detector & residual image display 7 a-5 detects theabnormal transmission-condition on the basis of the ghost conditionimaging signal Sc′ produced from the ghost-to-image converter 7 a-3.When detecting the abnormal state, it produces an abnormal state imagingsignal. When detecting no signal, it produces a level “Low”.

The abnormal state image integrator 7 a-6 adds thetransmission-condition imaging signal produced from the image integrator7 a-4, and the abnormal state imaging signal produced from the abnormalstate detector & residual image display 7 a-5, and produces atransmission-condition imaging signal including the abnormal stateimaging signal.

FIG. 32 is a block diagram of the construction of the abnormal statedetector & residual image display 7 a-5. This construction will bedescribed.

The correlation output signal Sc, pulse FSTrc with frame period, andsynchronizing signal C.Sync are supplied to an abnormal state residualdisplay 7 a-5B.

The ghost imaging signal Sc′ is supplied to an abnormal state detector 7a-5A. The outputs C-S and C-H, which will be described later, from theabnormal state residual display 7 a-5B are supplied to the abnormalstate detector 7 a-5. The output ABN from the abnormal state detector 7a-5A is supplied to the abnormal state residual display 7 a-5B, warningsound generator 7 a-5C and timer circuit 7 a-5D. The output G2 from thetimer circuit 7 a-5D is supplied to the abnormal state residual display7 a-5B.

The abnormal state detector 7 a-5A detects the position of ghostcondition imaging signal Sc′ displayed on the screen on the basis of theoutputs C-S and C-H which will be described later.

The abnormal state detector 7 a-5A, when the ghost imaging signal Sc′ isdisplayed at an abnormal position (for example, outside the guardinterval on the screen shown in FIG. 31), detects this situation asabnormal state, and produces ABN of level “High”. When it is displayedat a normal position, for example, within the guard interval, theabnormal state detector 7 a-5A detects this situation as normal state,producing signal ABN of level “Low”.

The abnormal state imaging signal CNT from the abnormal state residualdisplay 7 a-5B is level “Low” when the signal ABN is level “Low” (normalstate). When the signal ABN is level “High” (when abnormal state isdetected), the abnormal state residual display 7 a-5B generates the CNTof level “High” as described later.

The warning sound generator 7 a-5C generates warning sound ALARM whenthe signal ABN is High level. The timer circuit 7 a-5D controls the waythat the abnormal state imaging signal CNT is displayed. For example, itcontrols this signal to be continuously displayed for a predeterminedtime or to be intermittently displayed in a blinking manner for acertain time just before the displaying ends.

FIG. 33 is a block diagram of one example of the construction of theabnormal state residual display 7 a-5B according to the invention. Thisexample will be described.

This construction corresponds to the addition of the FIFO write-incontroller 7 a-5-13 and gate 7 a-5-14 to the ghost-to-image converter 7a-3 shown in FIG. 27.

The correlation output signal Sc is supplied to, and converted by theA/D converter 7 a-5-1 into a digital correlation output signal DSc of,for example, 8 bits. The signal DSc is supplied to an FIFO 7 a-5-2.

The digital correlation output signal D′Schb from the FIFO 7 a-5-2 issupplied to a comparator 7 a-5-4. The ghost level signal LEhb from thecomparator 7 a-5-4 is supplied to a gate 7 a-5-5. The output Lehb′ fromthe gate 7 a-5-5 is supplied to the gate 7 a-5-14.

The pulse FSTrc with frame period is supplied to the FIFO write-incontroller 7 a-5-13. The outputs WRSTb and WEb from the FIFO write-incontroller 7 a-5-13 are supplied to the write-in reset terminal WR andwrite-in enable terminal WE of the FIFO 7 a-5-2, respectively.

The synchronizing signal C.Sync is supplied to a clock (CK) reproducer 7a-5-6, an HD extractor 7 a-5-7 and a VD extractor 7 a-5-8. The clockproduced from the CK reproducer 7 a-5-6 is supplied to a counter 7a-5-9. The output WE from the counter 7 a-5-9 is supplied to the FIFOwrite-in controller 7 a-5-13.

The output HD from the HD extractor 7 a-5-7 is fed to a counter 7a-5-10. The output C-S from the counter 7 a-5-10 is supplied to a firstdecoder 7 a-5-3.

The output VD from the VD extractor 7 a-5-8 is fed to a H-counter 7a-5-11. The output C-H from the H-counter 7 a-5-11 is supplied to thefirst decoder 7 a-5-3 and a second decoder 7 a-5-12.

The first decoder 7 a-5-3 supplies the read reset signal RRST to the RRterminal of the FIFO 7 a-5-2, and the read enable signal RE to the REterminal of the FIFO 7 a-5-2. The output G1 from the first decoder 7a-5-3 is fed to the gate 7 a-5-5. The output Dhh from the second decoder7 a-5-12 is supplied to the comparator 7 a-5-4.

The operation of the abnormal state residual display 7 a-5B will bedescribed. The same portions as those of the ghost-to-image converter 7a-3 shown in FIG. 27 will not be described because they operate in thesame way as those of the converter 7 a-3.

The FIFO 7 a-5-2 is an FIFO memory for storing the abnormal ghostimaging signal for a predetermined time.

The FIFO 7 a-5-2 makes normal writing-in operation when the transmissioncondition is normal, and updates the received digital correlation outputsignal DSc indicative of ghost status. When the transmission conditionis abnormal, the FIFO 7 a-5-2 stops write-in operation for a certaintime, and holds the abnormal ghost imaging signal waveform for a certaintime. The reading operation of the FIFO 7 a-5-2 is the same as in FIG.27. That is, it receives the signals RE and RRST for read control fromthe first decoder 7 a-5-3, and makes reading operation on a steadybasis.

The FIFO write-in controller 7 a-5-13 controls the writing-in operationof the FIFO 7 a-5-2 for storing the abnormal ghost imaging signal. Thewrite-in control signals WRSTb and WEb from the FIFO write-in controller7 a-5-13 switch between the writing operation and writing-stop operationas above in response to the output ABN from the abnormal state detector7 a-5A which will be described later.

The comparator 7 a-5-4 makes the same operation on the output D′Schbfrom the FIFO 7 a-5-2 as in FIG. 27. The gate 7 a-5-5 receives outputLEhb from the comparator 7 a-5-4 and forcibly makes it level “Low” inthe blanking period.

The gate 7 a-5-14 forcibly makes its output CNT level “Low” when thetransmission condition is normal, but processes the output Lehb′ fromthe gate 7 a-5-5 to produce abnormal imaging signal CNT only when thetransmission condition is abnormal.

The generation of the output Lehb′ as the abnormal imaging signal CNTwill be described with reference to the timing chart of FIG. 39.

FIG. 39 shows the waveforms of signals Dhh, D′Sch and LEh in theghost-to-image converter 7 a-3 shown in FIG. 27 in addition to otherwaveforms.

As described in FIG. 29, the decoder 7 a-5-3 responds to the inputcounter signals C-S and C-H to generate the read reset signal RRST thattakes level “Low” for one CK period of time at every Horizontal scanningof the interval from the m-th scanning line to the (m+n)-th scanningline. This signal initializes the read address to the FIFO 7 a-5-2 into0. In addition, the read enable signal RE that takes level “High” duringthe period from the m-th scanning line to the (m+n)-th scanning line isalso supplied to the FIFO 7 a-5-2, causing the read address to the FIFO7 a-5-2 to progress. Consequently, the signal D′Schb is read from theFIFO 7 a-5-2 as the abnormal imaging signal.

The decoder 7 a-5-12 responds to the input counter signal C-H togenerate level 1 a at the m-th scanning line, and then reduces itsoutput Dhh by i at every Horizontal scanning until level 1 a minus ni atthe (m+n)-th H.

The comparator 7 a-5-4 compares the output D′Schb from the FIFO 7 a-5-2and the output Dhh from the decoder 7 a-5-12, and produces the signalLEhb that takes level “High” when the condition of D′Schb>Dhh issatisfied.

In other words, as shown in FIG. 39, since the D′Schb is smaller thanDhh for all H period of the m-th scanning period, the signal LEhbremains level “Low”. Then, only during a short time t1 of 1 H period ofthe (m+l)-th scanning line, the D′Schb is larger than Dhh, and thus theLEhb becomes level “High”. During a relatively long time t2 of 1 H ofthe (m+2)-th scanning line, the condition of D′Schb>Dhh is satisfied,and thus the signal LEhb takes level “High”. Thereafter, after theseoperations are repeated, the abnormal state imaging signal waveform asthe signal LEhb can be expressed in a form of scanning-line structure asillustrated.

When the transmission condition is normal, the renewal data is writtenin the FIFO 7 a-5-2, and thus the output D′Schb remains the currentghost-status waveform. Therefore, the abnormal state imaging signal LEhbis produced as the same signal as the ghost condition imaging signalLEh. At this time, however, the gate 7 a-5-14 forcibly makes the signalLehb′ level “Low”, and thus the abnormal state imaging signal is notdisplayed when the state is normal.

FIG. 35 is a block diagram of one example of the specific constructionof the abnormal state detector 7 a-5A. This detector will be described.

This detector is constructed to divide the display screen into 8regions, A through H, as shown in FIG. 34, and detect a region in whichthe abnormal state imaging signal is displayed so that whether thetransmission condition is normal or abnormal can be known.

The ghost imaging signal Sc′ is supplied to the abnormality detectionsignal generator 7 a-5A-3. The signals C-S and C-H are fed together todecoders 7 a-5A-1, 7 a-5A-2. The eight output signals Ra, Rb, . . . , Rhfrom the decoder 7 a-5A-1, and the output signals RESET and F-END fromthe decoder 7 a-5A-2 are supplied to the abnormality detection generator7 a-5A-3. Here, the number of the output signals from the decoder 7a-5A-1 corresponds to that of the regions into which the display screenis divided.

The decoder 7 a-5A-1 responds to the signals C-S and C-H to produce theeight signals Ra, Rb, . . . , Rh that indicate the currently scannedregions of the display screen. If the region A of the eight regions inFIG. 34 is currently scanned, only signal Ra of the eight output signalsis level “High”, and the other signals Rb, Rc, . . . , Rh are level“Low”.

The decoder 7 a-5A-2 generates the signals RESET and F-END that arelevel “High” when the video signal is within the V-blanking period ataround the end of frame, and supplies them to the abnormality detectionsignal generator 7 a-5A-3, thereby updating its output signal ABN atevery frame unit.

FIG. 36 is a block diagram of one example of the specific constructionof the abnormality detection signal generator 7 a-5A-3. The ghostimaging signal Sc′ is fed to eight AND gates 5A-3-1.

The eight output signals Ra, Rb, . . . , Rh from the decoder 7 a-5A-1are supplied to the eight AND gates 5A-3-1, respectively.

The signal RESET is fed to eight SR flip-flop (SR/FF) 5A-3-2. The signalF-END is supplied to a D-flip-flop (D-FF) 5A-3-4.

The output signals from the eight AND gates 5A-3-1 are supplied to theeight SR/FF 5A-3-2, and the outputs from the SR/FF 5A-3-2 are suppliedto an abnormality condition detector 5A-3-3. The output S-ABN from theabnormality condition detector 5A-3-3 is fed to the D-FF 5A-3-4.

The eight AND gates 5A-3-1 take the logical products of the signal Sc′and signals Ra, Rb, . . . , Rh to produce logical product outputs ANDa,ANDb, . . . , ANDh, respectively.

When these output signals are supplied to the set terminals of thecorresponding SR/FF 5A-3-2, the SR/FF 5A-3-2 generate signals SRa, SRb,. . . , SRh that indicate the presence or absence of ghost conditionwaveform in each region. Each of these signals indicates that the ghostwaveform is displayed or not in the corresponding region when it islevel “High” or level “Low”, respectively.

The abnormality condition detector 5A-3-3 detects whether theabnormality condition has occurred in the ghost imaging signal Sc′, onthe basis of these signals SRa through SRh. Thus, the detector 5A-3-3generates the signal S-ABN that becomes level “High” when the abnormalcondition is detected, and level “Low” when it is not detected.

This signal S-ABN is supplied to the D-FF 5A-3-4, and the F-END signalis also applied thereto as an enable signal, so that the D-FF 5A-3-4generates the signal ABN that contains the abnormality detected resultupdated at every frame.

After the ABN signal is updated in response to the F-END signal, theSR/FF 5A-3-2 are reset by the RESET signal.

FIG. 37 is a block diagram of one example of the specific constructionof this abnormality condition detector 5A-3-3. This detector will bedescribed. The signal SRb is fed to a NOT gate 5A-3-3-1, the signal SRcto a NOT gate 5A-3-3-2, and the signal SRd to a NOT gate 5A-3-3-3. Thefive signals SRa, SRe, SRf, SRg, SRh are supplied to an AND gate5A-3-3-4.

The outputs SRb′, SRc′ and SRd′ from the NOT gates 5A-3-3-1, 5A-3-3-2,and 5A-3-3-3 are fed to the AND gate 5A-3-3-4.

This abnormality condition detector 5A-3-3 is designed so that forexample, the state in which the ghost waveform is displayed in theregions A and E through H of the eight regions A through H shown in FIG.34, but is not displayed in the regions B, C and D can be detected asabnormality.

Here, the range from region B to region D in FIG. 34 corresponds to theguard interval range in FIG. 31. Thus, when the peak of the correlationoutput waveform indicative of ghost status is displayed shifted more tothe left end (region A) of the display screen, or when it is displayedfar away out of the guard interval, the detector can detect that thetransmission condition is more seriously abnormal.

Thus, the abnormality condition detector 5A-3-3 makes NOT operation onthe signals SRb, SRc, SRd by the NOT gates 5A-3-3-1 through 5A-3-3-3,and takes the logical product of signals SRa, SRb′, SRc′, SRd′, SRethrough SRh by the AND gate 5A-3-3-4, to thereby detect whether theabnormality occurs in the ghost imaging signal, thus producing thesignal S-ABN.

This signal S-ABN becomes level “High” when an abnormality is detected,and level “Low” when no abnormality is detected.

The operation of the abnormality condition detector 5A-3-3 will bedescribed in more detail with reference to FIGS. 34 and 40.

Let us consider that as an example, the display screen is divided intoeight regions of A through H, and a ghost waveform is displayed as shownin FIG. 34. For the sake of simple explanation, the full screen isassumed to be displayed by six scanning lines without interlacedscanning. FIG. 40 is a timing chart of signals produced at this time.

The signals Ra through Rh are level “High” when the regions A through Hare scanned, respectively. The signal F-END becomes level “High” for apredetermined time in the V blanking period after the end of full-screenscanning. The signal RESET becomes level “High” for a certain time inthe V-blanking period after the signal F-END.

The signals SRa through SRh are level “High” when the signal Sc′ becomeslevel “High” and when each of the signals Ra through Rh is level “High”,respectively. The signal S-ABN becomes level “High” when the signals SRathrough SRh satisfy the above condition.

The signal ABN is the state of the signal S-ABN held (updated) by theleading edge of the signal F-END. The signals SRa through SRh are resetby the leading edge of the signal RESET, and thus the signal S-ABN isreset to be level “Low”.

FIG. 38 is a block diagram of one example of the construction of theFIFO write-in controller 7 a-5-13. This controller will be described.The signal FSTrc is supplied to a selector 7 a-5-13-2. The clock CK issupplied to a selector 7 a-5-13-3.

The signal ABN is supplied to the selectors 7 a-5-13-2, 7 a-5-13-3. Theoutputs WES and WRS from a write-in stop signal generator 7 a-5-13-1 arefed to the selectors 7 a-5-13-2, 7 a-5-13-3.

The ABN signal indicative of abnormality controls the selectors 7a-5-13-2, 7 a-5-13-3 to select ones of the input signals.

When the ABN is level “Low”, or when the transmission condition isnormal, the outputs WEb and WRb from the selectors 7 a-5-13-2, 7a-5-13-3 are signals FSTrc and CK, respectively. Thus, the FIFO 7 a-5-2shown in FIG. 33 is controlled to be normally written in.

When the ABN signal is level “High”, or when the transmission conditionis abnormal, the outputs WEb and WRb from the selectors 7 a-5-13-2, 7a-5-13-3 are the signals WES and WRS of level “High” from the write-instop signal generator 7 a-5-13-1. Thus, the FIFO 7 a-5-2 shown in FIG.33 is stopped from being written in.

A modification of the transmission-condition-to-image converter 7 a willbe described with reference to FIGS. 41 and 42.

A transmission-condition-to-image converter 7 a′ shown in FIG. 41 has aghost-to-image converter/abnormality detector & residual image display 7a-7 provided to include the operation blocks common to theghost-to-image converter 7 a-3 and abnormality detector & residual imagedisplay 7 a-5. FIG. 42 shows a specific construction of thisghost-to-image converter/abnormality detector & residual image display 7a-7.

As illustrated in FIG. 42, the A/D converter 7 a-5-1, decoders 7 a-5-3,7 a-5-12, CK reproducer 7 a-5-6, HD-extractor 7 a-5-7, VD-extractor 7a-5-8, counters 7 a-5-9, 7 a-5-10, and H-counter 7 a-5-11 can be omittedbecause they can be shared.

The operation of the transmission-to-video converter 7 a′ is the same asthe transmission-to-video converter 7 a, and thus will not be described.

Thus, according to the transmission-to-video converters 7, 7 a, 7 a′ andtransmission image superimposing device 7 b mentioned above, since theghost imaging signal, BER imaging signal and filed intensity imagingsignal are displayed on a video monitor, the conditions, or status ofthe imaging signals can be comprehensively viewed in associated witheach other, so that the transmission condition can be correctly grasped.However, we further need to consider the following points.

Recently, there is a trend toward the change of length of the guardinterval (GI) as a buffer band against the mixing of reflected wavesaccording to the transmission situations in order to cope with varioustransmission conditions.

That is, for example, a signal format of more adequate GI length isselected according to the information contents being transmitted, andtransmission conditions from one signal format in which a guard intervalwaveform of 48 samples is added to the time base waveform of 1024samples to form a time base waveform of 1072 samples/symbol in total,and the other signal format in which a guard interval waveform of 96samples is added thereto to form a time base waveform of 1120samples/symbol in total.

When the GI length is changed according to transmission conditions byswitching, a GI mode signal for determining the GI length is supplied tothe transmission path encoder and guard adder of the transmitting-sideprocessor 101, and to the synchronizing detector & correlator andtransmission path decoder of the receiving-side processor 203, shown inFIGS. 1 and 17, thereby changing the GI length.

However, the transmission-condition-to-image converters 7, 7 a, 7 a′ andtransmission image superimposing device 7 b do not consider thetransmission mode for changing the GI length according to thetransmission situations, and the GI mode signal is not applied.Therefore, when the GI length is changed, the guard interval displayedat the position corresponding to the ghost imaging signal waveformcannot be changed in association therewith, and thus the transmissioncondition cannot be correctly understood.

Thus, according to the invention, a transmission-condition-to-imageconverter is proposed which can solve the above problem so that theguard interval can be displayed at the position corresponding to theghost imaging signal waveform even when the GI length is changed, andhence that the transmission condition can be correctly grasped. Thisconverter will be described with reference to FIGS. 43 through 52.

The transmission-condition-to-image converter is given a function tochange the display position range in which the guard interval isdisplayed according to the change of the GI length by switching. Thus,even when the GI length is changed, the positional range in which theguard interval is displayed can be automatically changed by thisfunction in association with the ghost imaging signal.

FIG. 43 is a block diagram of the construction of atransmission-condition-to-image converter 7 c capable of automaticallydetecting the GI mode signal, according to the invention. The portionsequivalent to those in the transmission-condition-to-image converter 7shown in FIG. 2A will not be described.

The correlation output signal Sc and pulse FSTrc with frame period aresupplied to a ghost-to-image converter 7 c-3. The FSTrc signal is alsofed to a guard interval mode detector 7 c-8. The output, GI mode signalfrom the guard interval mode detector 7 c-8 is supplied to theghost-to-image converter 7 c-3 and an image integrator 7 c-4. The outputfrom the ghost-to-image converter 7 c-3 is supplied to the imageintegrator 7 c-4.

The synchronizing signal C.Sync from the image integrator 7 c-4 is fedto the sync input terminals of a field-intensity-to-image converter 7c-1, a BER-to-image converter 7 c-2 and the ghost-to-image converter 7c-3. The image integrator 7 c-4 generates a transmission-conditionimaging signal.

The field-intensity-to-image converter 7 c-1, BER-to-image converter 7c-2, ghost-to-image converter 7 c-3 convert signals of differenttransmission conditions to imaging signals according to thesynchronizing signal C.Sync, respectively. The image integrator 7 c-4combines the imaging signals, and adds a sync signal for video image tothose combined imaging signals. Or this integrator superimposes thoseimaging signals on an externally applied video signal.

The guard interval mode detector 7 c-8 detects the GI mode correspondingto the guard interval length, and sends the resulting GI mode signal toassociated blocks.

The transmission-condition-to-image converter 7 c of this constructionautomatically detects the GI mode signal corresponding to the range ofthe guard interval from the FSTrc signal by use of the guard intervaldetector 7 c-8. In addition, the converter 7 c changes the displayedrange and length of the guard interval, the range (alarm range) in whichany one or more transmission conditions are abnormal, and the samplingperiod of correlation output signal Sc by switching in accordance withthe GI mode signal.

FIG. 44A shows an example of the screen displayed when the guardinterval is 3 μsec. In this case, the guard interval length is threegraduations, and the alarm range is out of the guard interval.

FIG. 44B shows an example of the screen displayed when the guardinterval is 6 μsec. In this case, the guard interval is as long as 6graduations, and the alarm range is displayed narrower on the right sideof the screen away from the guard interval.

FIG. 45 is a block diagram of a specific construction of the guardinterval mode detector 7 c-8. The FSTrc signal is supplied to the resetterminal of a counter 7 c-8-1 and the enable terminal of a latch 7c-8-2. The output terminal of the counter 7 c-8-1 is connected to theD-input terminal of the latch 7 c-8-2. A clock (CK) source 7 c-8-4 isconnected to the CK input terminal of the counter 7 c-8-1. The outputterminal of the latch 7 c-8-2 is connected to the input terminal of adeterminer 7 c-8-3.

The operation of the guard interval mode detector 7 c-8 will bedescribed. If the CK frequency of the CK source 7 c-8-4 is 16 MHz, sincethe FSTrc signal occurs with a period of 60.3 m sec, the maximum valuethat the counter 7 c-8-1 counts is about 964800.

The counter 7 c-8-1 is once reset by the next FSTrc signal into 0, butthe latch 7 c-8-2 holds the value just before the resetting, or themaximum value of the counter 7 c-8-1.

Therefore, since the determiner 7 c-8-3 detects the value of the outputPK from the latch 7 c-8-2, the associated guard interval can bedetermined.

Since the maximum value of 964,800 is not always produced depending onthe frequency accuracy of the CK source 7 c-8-4, an allowance of ±21,600is given for the determination.

FIG. 46A shows the relation among the FSTrc, the counter output and thelatch output when the maximum value of the counter 7 c-8-1 is about964,800 that corresponds to a guard interval of 3 μsec.

FIG. 46B shows the relation among the FSTrc, the counter output and thelatch output when the maximum value of the counter 7 c-8-1 is about1,008,000 that corresponds to a guard interval of 6 μsec.

Thus, the GI mode can be decided by discriminating the output values ofthe latch 7 c-8-2, or the maximum values of the counter 7 c-8-1.

FIG. 47 is a block diagram of a specific construction of theghost-to-image converter 7 c-3. This converter will be described. The CKsignal from a CK reproducer 7 c-3-6 is supplied to a counter 7 c-3-9.The GI mode signal is supplied to the counter 7 c-3-9. The output WEsignal from the counter 7 c-3-9 is fed to the WE terminal of an FIFO 7c-3-2.

Since the change of the correlation output signal Sc usually depends onthe symbol period, the increase of the guard interval length (from 3μsec to 6 μsec) will result in the change of ghost imaging signal from67 μsec to 70 μsec.

The counter 7 c-3-9 changes the period with which the WE signal occursin accordance with that change, and hence the sampling period is changedaccording to the GI mode signal.

FIG. 48 shows a specific construction of the counter 7 c-3-9. Referringto FIG. 48, the CK signal is supplied to the CK terminal of a counter 7c-3-9-1. The output from the counter 7 c-3-9-1 is fed to a decoder 7c-3-9-2.

The output from the decoder 7 c-3-9-2 is supplied to the reset terminalRST of the counter 7 c-3-9-1, and to the outside as the WE signal. TheGI signal is supplied to the decode value switching terminal of thedecoder 7 c-3-9-2.

The operation of each part of the counter 7 c 3-9 will be described. Thecounter 7 c-3-9-1 counts the CK signal when the reset terminal RST is atlevel “High”.

The decoder 7 c-3-9-2 generates, for example, level “Low” when 1,071 for1,072 samples/symbol or 1,119 for 1,120 samples/symbol is appliedaccording to the GI mode signal. When the reset terminal is at level“Low”, the content of the counter 7 c-3-9-1 is reset back to zero.

The result is that the counter 7 c-3-9-1 repeats counting 0˜1,071 or0˜1,119.

FIG. 49A shows the output WE from the counter 7 c-3-9 when the guardinterval is 3 μsec. As shown in FIG. 49A, the WE signal becomes level“Low” with a period of 67 μsec.

FIG. 49B shows the output WE from the counter 7 c-3-9 when the guardinterval is 6 μsec. From FIG. 49B, it will be seen that the WE signalbecomes level “Low” with a period of 70 μsec.

FIG. 50 is a block diagram of a specific construction of the imageintegrator 7 c-4. The field intensity imaging signal, BER imaging signaland ghost imaging signal are supplied to an adder 7 c-4-6 via gates 7c-4-1, 7 c-4-2 and 7 c-4-3, respectively.

A display selector 7 c-4-4 generates add-on/off signals that control thefield intensity imaging signal, BER imaging signal and ghost imagingsignal to be separately added or not, respectively.

The GI mode signal is fed to an external video sync type synchronizingsignal generator 7 c-4-5. The video signal is supplied to the externalvideo sync type synchronizing signal generator 7 c-4-5 and adder 7c-4-6. The external video sync type synchronizing signal generator 7c-4-5 supplies the synchronizing signal C.Sync to the outside. It alsosupplies a display signal of the time scale and guard interval to theadder 7 c-4-6.

The gates 7 c-4-1, 7 c-4-2, 7 c-4-3 are controlled by the displayselector 7 c-4-4 to allow the input imaging signals to be passedtherethrough or not. The signals passed through the gates 7 c-4-1, 7c-4-2, 7 c-4-3 are added together with the C.Sync signal, by the adder 7c-4-6, to produce the transmission-condition imaging signal.

An example of the addition rates of signals in the adder 7 c-4-6 will beshown. If the signals to be applied are all +5 Volts in digital level,the rates of the field intensity imaging signal, BER imaging signal andghost imaging signal are 0.2, the rates of the time scale signal andguard interval signal are 0.05, and the rate of the C.Sync signal is0.1. Thus, the imaging signal of about 1 Volt_(p-p) including the syncportion can be produced.

FIG. 51 is a block diagram of a specific construction of the externalvideo sync type synchronizing signal generator 7 c-4-5. This generatorwill be described.

A sync extractor 7 c-4-5-1 extracts an extracted sync signal from theinput video signal. This sync signal is supplied to a counter 7 c-4-5-2.The counter 7 c-4-5-2 is reset by the vertical sync signal. The outputfrom the counter 7 c-4-5-2 is fed to decoders 7 c-4-5-3, 7 c-4-5-4, 7c-4-5-5.

The outputs of, for example, 3 μsec, 6 μsec and 12 μsec of guardinterval length, from the decoders 7 c-4-5-3, 7 c-4-5-4 and 7 c-4-5-5are supplied to a selector (SEL) 7 c-4-5-6, and thereby any one isselected in accordance with the GI mode signal as an output of eachdifferent guard interval length.

FIG. 52A shows a guard interval length signal of 3 μsec. In thisexample, this signal is displayed as a band shape of a range surroundedby the 220-th and 230-th scanning lines as counted from the bottom ofthe display screen, and by the 400-th and 580-th pixels in the lateraldirection.

FIG. 52B shows a guard interval length signal of 6 μsec. In thisexample, this signal is displayed as a band shape of a range surroundedby the 220-th and 230-th scanning lines as counted from the bottom ofthe display screen, and by the 400-th and 760-th pixels in the lateraldirection.

The alarm ranges shown in FIGS. 44A and 44B are switched by the samemethod. Although this embodiment automatically detects the guardinterval, and switches modes for each portion, the GI mode signal may bechanged manually.

According to the embodiments of the invention mentioned above, since adigital transmission system can be produced in which the fieldintensity, BER and ghost status indicative of the levels/presence orabsence of reflected waves can be converted to differenttransmission-condition imaging signals and displayed so that thosetransmission-condition imaging signals or plus the received/decodedvideo signal can be comprehensively observed in association with eachother, the alignment operation can be more correctly and easilyperformed. In addition, a digital transmission system having thefunction to alarm when the transmission condition is abnormal can beproduced, and thus the transmission path characteristics can be graspedmore correctly and easily.

While the OFDM system digital transmission has been described as anexample, the present invention can be applied not only to thismulti-carrier system such as OFDM but also to a single-carrier digitalsystem. The following example can be considered as the ghost statussignal detection method in the single-carrier system.

Ghost information is derived from the received signal byself-correlation processing and by using the preamble waveform componentin a transmission system including a symbol mode in which the modulatedsignal includes periodical waveform components with respect to time, forexample, in the single QAM system disclosed in U.S. Pat. No. 5,946,350.

With reference to drawings, a description will be made of an embodimentin which the ghost status imaging signal, and BER and field intensityimaging signals are transmitted together with the video signals that aretransmitted from the outside broadcast vans 51 and 52 via the relayingstation 53 to the broadcast station 54 as shown in FIG. 53. In thisembodiment, since the program director in the broadcast station 54 canview the information of ghost status, BER and field intensity on thedisplay, he can correctly and easily decide to select a satisfactorilytransmitted video signal from the video signals that are transmittedfrom a plurality of outside broadcast vans. Like elements correspondingto those in the above-mentioned embodiments have fundamentally the samefunctions, and thus will not be described.

FIG. 55 is a block diagram of the whole construction of anotherembodiment according to the invention. FIGS. 56A, 56B and 56C showoutput video signals at each portion and displayed screens,respectively. This embodiment will be described in detail.

The transmission side such as outside broadcast vans has the MPEG-ENC101M and the transmission-side processor 101. The receiving side of thefirst relaying station built on, for example, a hill has thereceiving-side processor 203, the MPEG-DEC 203M, and thetransmission-condition images superimposing device 7T. The signalprocessings from the transmission-side processor 101 to thereceiving-side processor 203, and to transmission-condition imagessuperimposing device 7T are the same as in the embodiment described withreference to FIG. 1 or FIG. 16.

The AGC control signal Sa indicative of a received field intensity,correlation-calculated signal Sc indicative of mixture status ofreflected waves (ghost), and signal Sb indicative of BER status, whichare produced from the receiving-side processor 203, are supplied to thetransmission-condition images super-imposing device 7T. The FSTrc pulseas the operation timing reference from the receiving-side processor 203is also supplied to the transmission-condition images superimposingdevice 7T. The video output V_(i) (FIG. 56A) from the MPEG-ENC 203M isfed as the video signal to the transmission-condition imagessuperimposing device 7T. The video output V_(i) is not limited to theoutput from the MPEG-ENC 203M, but may be an externally fed video signalfrom other video apparatus.

The video signal and audio signal received by the receiving-side of therelaying station are transmitted directly or via a plurality of otherrelaying stations (not shown) to the final receiving station, orbroadcast station having studios. This transmission is made by means of,for example, analog FPU of microwave band.

The superimposed information extractor & transmission-condition-to-imageconverter 7R is provided on the final receiving station, or studio side.

The transmission-condition images superimposing device 7T receives thecorrelation-calculated signal Sc indicative of the mixture of reflectedwaves (ghost-status), and signals Sa indicative of the field strength,Sb indicative of the BER state together with the reference signal FSTrcindicative of pulses in frame period from the receiving-side processor203, and it superimposes the information of these transmissionconditions on the vertical blanking (VBL) period, out of the videoeffective period, of the video signal (FIG. 56A) that is fed from theMPEG-ENC 203M. The video signal Vs (FIG. 56B) with thetransmission-conditions information superimposed is transmitted from apredetermined video transmitter 203T to the studio side.

On the studio side, a predetermined video receiver 300 produces a videosignal Vs′ by receiving the transmitted signal from the relayingstation. The superimposed information extractor &transmission-condition-to-image converter 7R extracts, from the videosignal Vs′, information Sa′, Sb′ and Sc′ indicative oftransmission-conditions superimposed on the VBL period. Then, itreceives the extracted information Sa′, Sb′ and Sc′ indicative of thetransmission conditions according to the synchronizing signal C.Sync,and outputs those information as a transmission-condition imaging signalto display 11 according to the synchronizing signal C.Sync within thevideo effective period which will be described later.

This transmission-condition imaging signal is displayed on the displayas shown in FIG. 56C.

The construction of the transmission-condition images superimposingdevice 7T is fundamentally the same as in FIG. 11, but the constructionof the image integrator 7-4 is slightly changed in this superimposingdevice 7T.

FIG. 57 is a block diagram of an example of the image integrator 7-4.This integrator will be described in detail.

The video signal is supplied to an external video sync typesynchronizing signal generator 7-4-5 a and the adder 7-4-6. Thesynchronizing signal C.Sync from the generator 7-4-5 a is fed to theoutside. The adder 7-4-6 adds the imaging signals passed through thegates 7-4-1, 7-4-2, 7-4-3, the signal indicative of the time base scaleand guard interval relative to the ghost imaging signal, and the videosignal to produce the transmission-condition superimposed video signalVs. A superimposing position pulse generator 7-4-4 a specifies theposition at which each imaging signal is superimposed on the videosignal.

An example of the addition rates in the adder 7-4-6 will be given. Ifall signals applied to the adder 7-4-6 are +5 Volts in digital level,the rates of the field-intensity imaging signal, BER imaging signal andghost imaging signal are 0.2, the rates of the time base scale signaland guard interval range signal are 0.05, and the rate of the videosignal of which the video portion is analog signal of about 0.7 Volts isone.

FIG. 58 shows one example of the waveform of the transmission-conditionsuperimposed video signal Vs. From FIG. 58, it will be seen that theghost imaging signal Psc, field intensity imaging signal Sa0 throughSa5, and BER imaging signal Sb0 through Sb5 are superimposed on the VBLperiod of one line.

Since the ghost imaging signal is super-imposed in analog level, theamplitude of the ghost waveform can be expressed by continuous curveswith peaks. The field intensity level and BER can be expressed by binaryvalues of which “0” or “1” indicates the presence or absence of theamplitude. That is, the presence or absence of amplitude is expressed byvalue “0” or “1” of digitized information.

FIG. 59A is a block diagram of an embodiment of thefield-intensity-to-image converter 7-1. This converter will bedescribed.

The control signal Sa indicative of a field intensity is supplied to,and converted by the A/D converter 7-1-1 into the digital signal DSa of,for example, 6 bits. The signal DSa indicative of the field intensity isfed to, and converted by the decoder (DEC) 7-1-2 into, for example, allsix signals of DSa0 through DSa5. The output signals DSa0 through DSa5are fed to one terminals of the six AND gates (AND) 7-1-4, respectively.The six output signals from the AND 7-1-4 are supplied to the OR gate(OR) 7-1-5. The synchronizing signal C.Sync is fed to the superimposingposition pulse generator 7-1-3 a, which then generates associatedsuperimposing position pulses a0 through a5 in synchronism with thesynchronizing signal C.Sync. The pulses a0 through a5 are supplied tothe other terminals of the AND 7-1-4, which then take the logicalproducts of them and signals DSa0 through DSa5.

If the signal DSa indicative of the field intensity is 00 h, or 0 indecimal notation, only the signal Da0 becomes level “High”, and thusonly the product of the pulse a0 and signal DSa0 is level “High”, withthe result that only the signal DSa0 of the position corresponding tothe pulse a0 is produced. If the signal DSa is 03 h, or 3 in decimalnotation, the products of DSa0 through DSa3 and a0 through a3 are level“High”, so that the signals DSa0 through DSa3 of the positionscorresponding to the pulses a0 through a3 are produced. Then, thoseoutput signals from the AND are logically processed in the OR 7-1-5 toproduce the field intensity imaging signals Sa0 through Sa5.

Here, If the pulse a0 corresponds to the position of the 12-th H, andthe 512-nd through 520-th sample, pulse al the position of the 12-th H,and 521-st through 529-th sample, and pulse a5 the position of the 12-thH, and the 540-th through 548-th sample, the field intensity imagingsignal Sa0 through Sa5 is superimposed on the VBL period, out of thevideo effective area, of the video signal as shown by the rasterscanning screen of FIG. 59B.

FIG. 60A is a block diagram of an embodiment of the BER-to-imageconverter 7-2. This converter will be described.

The signal Sb indicative of BER is supplied to, and converted by the A/Dconverter 7-2-1 into the digital signal DSb of about 3 bits. The signalDSb indicative of the BER is converted by the decoder (DEC) 7-2-2 into,for example, all five signals DSb0 through DSb4.

The output signals DSb0 through DSb4 are fed to one input terminals ofthe five AND gates (AND) 7-2-4. The five output signals from the AND7-24 are supplied to the OR gate (OR) 7-2-5.

The synchronizing signal C.Sync is supplied to a superimposing positionpulse generator 7-2-3 a, which then generates pulses b0 through b4 forsuperimposing the BER signal according to the timing of thesynchronizing signal C.Sync.

The pulses b0 through b4 are fed to the other input terminals of the AND7-2-4, which then take the logical products of the signals DSb0 throughDSb4 and the pulses b0 through b4. Here, if the BER signal DSb is 00 h,or 0 in decimal notation, only the signal DSb0 is level “High”, and thusonly the product of the pulse b0 and signal DSb0 is level “High”, sothat the signal DSb0 of the position corresponding to the pulse b0 isproduced. If the signal DSb is 03 h, or 3 in decimal notation, the logicproducts of the DSb0 through DSb3 and b0 through b3 are level “High”,with the result that the signals DSb0 through DSb3 of the positionscorresponding to the pulses b0 through b3 are produced.

The superimposing position pulse generator 7-2-3 a, if it is for NTSC,makes logical processing by use of the 1/910 frequency dividing counterthat counts at a clock of 14.3 MHz and is reset with a H-period, and the1/525 frequency dividing counter that counts at a clock of 1/2 H and isreset with V-period.

Thus, as, for example, illustrated on the raster screen of FIG. 60B, theb4 signal corresponds to the position of the 12-th H, and 560-th through567-th sample, and the b3 signal the position of the 12-th H, and 568-ththrough 575-th sample. The b2 signal corresponds to the position of the12-th H, and the 576-th through 583-rd sample, the b1 signal theposition of the 12-th H, and the 584-th through 591-st sample, and theb0 signal the position of the 12-th H, and the 592-nd through 599-thsample. Therefore, at this time, the BER imaging signal Sb0 through Sb4is superimposed on the VBL period, out of the effective area, of thevideo signal as shown in FIG. 60B.

FIG. 61 is a block diagram of an embodiment of the ghost-to-imageconverter 7-3. This converter will be described.

The correlation output signals indicative of the ghost status issupplied to, and converted by the A/D converter 7-3-1 into the digitalcorrelation output signal DSc of 8 bits. This signal DSc is fed to theFIFO 7-3-2. The pulse FSTrc of frame period is supplied to the write-inreset terminal of the FIFO 7-3-2. The digital correlation output signalD′Sc from the FIFO 7-3-2 is fed to the D/A converter 7-3-7. The outputfrom the D/A converter 7-3-7 is produced as the ghost imaging signalPsc. The synchronizing signal C.Sync is supplied to the timing pulsegenerator 7-3-3.

The generator 7-3-3 responds to the synchronizing signal C.Sync togenerate the read reset signal RRST and read enable signal RE, andsupply them to the FIFO 7-3-2.

FIG. 62 is a timing chart for the relation among the signal C.Sync,signal RRST, signal RE and ghost imaging signal Psc. The operation ofthe converter will be described.

The timing pulse generator 7-3-3 generates the reset signal RRST at thetime of the 12-th H, and the 128-th sample in each video period, so thatthe FIFO 7-3-2 can be made ready to read the written contents from thebeginning end. In addition, it generates the RE signal that becomeslevel “Low” at the time of the 12-th H, and the 130-th through 400-thsample, so that the contents (D′Sc) written in the FIFO 7-3-2 can beread in turn according to this signal.

The readout signal D′Sc is converted by the D/A converter 7-3-7 into theanalog ghost imaging signal Psc, which is produced in the VBL period ofeach video period.

FIG. 63A is a block diagram of the superimposed information extractor &transmission-condition-to-image converter 7R as another example. Thisconverter will be described.

The superimposed information extractor & transmission-condition-to-imageconverter 7R to which the video signal Vs′ in which thetransmission-condition information sa0′ through sa5′, sb0′ through sb4′,Psc′ are superimposed on the VBL period is supplied has a superimposedfield-intensity extractor & field-intensity-to-image converter 7-1V, asuperimposed BER extractor & BER-to-image converter 7-2V, a superimposedghost extractor & ghost-to-image converter 7-3V, and an image integrator7-4V.

The synchronizing signal C.Sync is derived from the video signal Vs′ inthe image integrator 7-4V, and supplied from the image integrator 7-4Vto the superimposed field-intensity extractor & field-intensity-to-imageconverter 7-1V, superimposed BER extractor & BER-to-image converter7-2V, and superimposed ghost extractor & ghost-to-image converter 7-3V.

The outputs V0Sa, V0Sb, V0Sc from those extractor & converters 7-1V,7-2V, 7-3V are supplied to the image integrator 7-4V.

The extractor & converters 7-1V, 7-2V, 7-3V find, in synchronism withthe synchronizing signal C.Sync, the periods of the information sa0′through sa5′, sb0′ through sb4′, Psc′ that are indicative of thetransmission-conditions superimposed on the VBL period of the inputvideo signal Vs′, and extracts these information. In addition, thoseextractor & converters 7-1V, 7-2V, 7-3V convert these information to theassociated imaging signals so that they can be displayed onpredetermined positions within the video effective period as will bedescribed later.

The image integrator 7-4V unites these imaging signals to form thetransmission-condition imaging signal.

FIG. 63B is a schematic diagram showing this transmission-conditionimaging signal (Vosa, Vosb, Vosc) fed to and displayed on a display 11(FIG. 55) within the video effective period of the screen. Thus, sincethe various different transmission conditions (field intensity-Vosa,BER-Vosb, ghost-Vosc) are displayed within the video effective period ofthe screen, the director or operator on the studio side distant awayfrom the OFDM transmission system can correctly grasp the transmissionconditions, or transmission status.

FIG. 64A is a block diagram of an example of the superimposed fieldintensity extractor & field-intensity-to-image converter 7-1V. Thisconverter will be described.

The analog field intensity information sa0′ through sa5′ superimposed onthe 12-th H of the video signal Vs′ as described above is supplied to acomparator 7-1V-1, and converted thereby into digital signals Dsa0′through DSa5′. These signals Dsa0′ through DSa5′ are serially successivesignals with respect to time.

The signals Dsa0′ through DSa5′ are fed to a serial-to-parallelconverter (S/P) & latch 7-1V-1, and converted thereby to parallel dataDSa [5:0] P′ of, for example, 6 bits.

The sampled, held parallel output DSa [5:0] P′ from the S/P & latch7-1V-1 is supplied to a decoder 7-1V-2. The decoder 7-1V-2 converts theDSa [5:0] P′ of 6 bits to, for example, 64 pieces of data, DSa63′through Dsa0′.

The outputs DSa63′ through Dsa0′ from the decoder 7-1V-2 are supplied to64 AND gates 7-1V-4, respectively. The outputs from the 64 AND gates7-1V-4 are fed to an OR gate 7-1V-5. The synchronizing signal C.Sync issupplied to a superimposed field intensity extractor & display positionpulse generator 7-1V-3. This extractor & pulse generator 7-1V-3 respondsto the synchronizing signal C.Sync to generate the extraction pulse Psaand display position pulses a63′ through a0′.

A total of six pulses of the extraction pulse Psa are generated duringthe interval, for example, from the 512-nd to 548-th sample of 12-th Hout of the video effective period. The display position pulses a0′through a63′ become level “High” during the positional range, forexample, from the 200-th to 203-rd horizontal scanning line, and fromthe 384-th to 640-th sample.

That is, the signal a0′ is displayed at the position of the 200-ththrough 203-rd H (Horizontal line), and the 384-th to 387-th sample. Thesignal a62′ is displayed at the position of the 200-th through 203-rd H,and the 632-nd through 635-th sample.

The signal a63′ is displayed at the position of the 200-th to 203-th H,and the 637-th through 640-th sample.

These pulses a0′ through a63′ are supplied to the other input terminalsof the AND gates 7-1V-4. The AND gates 7-1V-4 produce the logic productsof the pulses a0′ through a63′ and DSa63′ through Dsa0′, respectively.

FIG. 64B is a schematic diagram showing the extraction pulse Psa anddisplay position pulses a0′ through a63′ displayed on the screen.

FIG. 65A is a block diagram of an embodiment of the superimposed BERextractor & BER-to-image converter 7-2V. This extractor & converter 7-2Vwill be described.

The analog BER information Sb0′ through Sb4′ superimposed on the 12-th Hof the video signal Vs′ as described above are supplied to a comparator7-2V-1, and converted thereby to digital signals DSb0′ through DSb4′.The signals DSb0′ through DSb4′ are a total of five serially successivesignals with respect to time. The signals DSb0′ through DSb4′ aresupplied to a serial-to-parallel converter (S/P) & latch 7-2V-2, andconverted thereby to, for example, a total of five parallel pieces ofdata DSb0′ through DSb4′.

The signals DSb0′ through DSb4′ from the S/P & latch 7-2V-2 are fed tofive AND gates 7-2V-4. The five outputs from the AND gates 7-2V-4 aresupplied to an OR gate 7-2V-5.

The synchronizing signal C.Sync is supplied to a superimposed BERextractor & display position pulse generator 7-2V-3. The extractor &generator 7-2V-3 responds to the synchronizing signal C.Sync to generatedisplay position pulses b0′ through b4′ during the video effectiveperiod. This extractor & generator 7-2V-3 also generates the extractionpulse PSb′ at the 12-th H out of the video effective period.

FIG. 65B is a schematic diagram showing the extraction pulse PSb anddisplay position pulses b0′ through b4′ displayed on the screen.

The superimposed BER extractor & display position pulse generator7-2V-3, if it is used for NTSC, makes logic processing by use of a 1/910frequency dividing counter that counts at a clock of 14.3 MHz and isreset with H-period, and a 1/525 frequency dividing counter that countsat a clock of 1/2 H and is reset with V-period.

Consequently, for example, the signal b4′ is displayed at the positionof the 80-th through 96-th H, and the 512-nd through 526-th sample. Thesignal b3′ is displayed at the position of the 80-th through 96-th H,and 528-th through 542-nd sample. The signal b2′ is displayed at theposition of the 80-th through 96-th H, and the 544-th through 558-thsample. The signal b1′ is displayed at the position of the 80-th through96-th H, and the 560-th through 574-th sample. The signal b0′ isdisplayed at the position of the 80-th through 96-th H, and the 576-ththrough 590-th sample.

FIG. 66A is a block diagram of an embodiment of the superimposed ghostextractor & ghost-to-image converter 7-3 V. This extractor & converter7-3 V will be described.

The ghost information PSc′ superimposed at the 12-th H of the videosignal Vs′ as described above is supplied to an A/D converter 7-3V-1.The output D′Sc from the A/D converter 7-3V-1 is fed to the write-indata terminal of an FIFO 7-3V-2. The output D′Sch from the FIFO 7-3V-2is supplied to a comparator 7-3V-4. The output LE from the comparator7-3V-4 is supplied to a gate 7-3V-5.

The synchronizing signal C.Sync is supplied to a CK reproducer 7-3V-6,an HD extractor 7-3V-7, and a VD extractor 7-3V-8. The output CK fromthe CK reproducer 7-3v-6 is fed to a counter 7-3V-9. The output WE fromthe counter 7-3V-9 is supplied to the WE terminal of the FIFO 7-3V-2.

The output HD from the HD extractor 7-3V-7 is supplied to a counter7-3V-10. The output C-S from the counter 7-3V-10 is fed to a decoder7-3V-3. The output VD from the VD extractor 7-3V-8 is supplied to anH-counter 7-3V-11. The output C-H from the H-counter 7-3V-11 is suppliedto the decoder 7-3V-3 and a decoder 7-3V-12. The output RRST from thedecoder 7-3V-3 is supplied to the RR terminal of the FIFO 7-3V-2.Similarly, the output RE from the decoder 7-3V-3 is fed to the REterminal of the FIFO 7-3V-2.

The control signal WRST for use in extracting the ghost information PSc′is supplied from the decoder 7-3V-3 to the write-in reset terminal WR ofthe FIFO 7-3V-2. The WE is fed to the write-in control terminal WE ofthe FIFO 7-3V-2. The output Dhh from the decoder 7-3V-12 is fed to thecomparator 7-3V-4.

The CK reproducer 7-3V-6 reproduces the CK of, for example, 14.3 MHz onthe basis of the input synchronizing signal C.Sync. The HD extractor7-3V-7 extracts the H-period component from the synchronizing signalC.Sync, and produces the HD signal of H-period. The counter 7-3V-10 isreset by the HD signal and produces the counter signal C-S of which thevalue increases at every CK period.

The VD extractor 7-3V-8 extracts the V-period component from thesynchronizing signal C.Sync, and produces the VD signal of V-period. TheH-counter 7-3V-11 is reset by the VD signal, and produces the countersignal C-H of which the value increases at every H-period.

The decoder 7-3V-3 receives the counter signals C-S and C-H, andproduces on the basis of those signals the read reset signal RRST thatbecomes level “Low” for 1 CK period at every Horizontal scanning lineduring the interval from the m-th scanning line to the (m+n)-th scanningline. This RRST initializes the read address to the FIFO 7-3V-2 into 0.The decoder 7-3V-3 also produces the read enable signal RE that becomeslevel “High” during the interval, similarly, from the m-th scanning lineto the (m+n)-th scanning line, and advances the read address to the FIFO7-3V-2 so that the D′Sch as the correlation calculated signal Sc can beread from the FIFO 7-3V-2.

The decoder 7-3V-12 responds to the input counter signal C-H to generatethe Dhh that becomes level 1 a at the m-th scanning line, then reducesits level by i at every horizontal scanning line, and becomes 1 b at the(m+n)-th scanning line. The comparator 7-3V-4 compares the D′Sch as thecorrelation calculated signal Sc and the Dhh, and produces output LEhthat becomes level “High” when the condition of D′sch>Dhh is satisfied.FIG. 66B shows the ghost imaging signal VOSC superimposed on thereproduced picture of the video signal on the display screen.

FIG. 67 is a timing chart of the various signals mentioned above. Theextractor & converter 7-3V will be further described.

The WRST signal is generated, for example, at the 100-th sample of the12-th H of the video signal Vs′ on which the information is superimposedat the 12-th H, and initializes the FIFO 7-3V-2. The WE signal isgenerated that becomes level “Low”, for example, in the interval fromthe 128-th to the 256-th sample of the 12-th H of the video signal Vs′on which the information is superimposed at the 12-th H, so that theD′Sc can be written in the FIFO 7-3V-2.

The RE signal is produced during the interval from the m-th to the(m+n)-th sample at every H-period, so that the written contents can beread sequentially one by one. The signal D′Sch read out at everyH-period of the video signal is compared with the value Dhh at everyhorizontal scanning line, so that the comparator generates the LE signalthat becomes level “High” when the condition of D′Sc<Dhh is satisfied.

In order to prevent the LE signal from being generated in the blankingperiod, the GI signal that becomes level “Low” during the blankingperiod is used to forcibly make the ghost imaging signal V0Sc level“Low” in the blanking period. The higher the level of the Sc signal, thelonger the High-level period of the ghost imaging signal.

Thus, the information of the field intensity, BER and reflected wavemixture (ghost) that indicate the transmission conditions, status orsituations in the transmission of signals from movable bodies can betransmitted to the studio side distant away from the OFDM transmissionsystem. On the studio side, each piece of the information that indicateseach of the superimposed transmission conditions is extracted from thereceived video signal, and displayed as a transmission-condition imagingsignal within the video effective period, so that the director oroperator can accurately understand these transmission conditions fromthe screen.

If the receiving side has no special receiver for the transmittedinformation indicative of the transmission conditions that require suchtransmission and displaying system as mentioned above, the operatorcannot view the transmission conditions.

Thus, the next embodiment, which will be described below, enables thedirector or operator to grasp the transmission conditions without anyspecial receiver by expressing the information of transmissionconditions in amplitude levels or in pulse width values, and adding, orsuperimposing them on part of the video signal before the transmissionof the information.

FIG. 69 schematically shows one example of the transmission-conditionsuperimposed & continuous signal added video signal that has addedtherein a signal Asa of the field intensity information Sa expressed byamplitude level intensity and a signal Asb of the BER information Sbsimilarly expressed by amplitude level.

There is a video waveform monitor that is always taken as an apparatusin the field of the operation on a mobile relaying communicator such asthe outside broadcast van. If this monitor is used for the operator toobserve only the signal of a line containing the transmission-conditionsuperimposed & continuous signal added video signal waveform by the lineselection function, the transmission conditions can be viewed orobserved without use of the special apparatus (the superimposedinformation extractor & transmission-condition-to-image converter 7R).

FIG. 68 is a block diagram an example of the construction of thecombination of a transmission-condition adder 7Tsub of the invention andthe transmission-condition image superimposing device 7T shown in FIGS.55 and 11. This construction will be described with reference to FIG.68.

The video signal that serves to carry the information of thetransmission conditions at the time of transmission is generated from avideo integrator 7 b-4 within the transmission-condition imagesuperimposing device 7T, and supplied to the i3 terminal of asuperimposing device 7-8 of the transmission-condition adder 7Tsub. Atransmission-condition superimposed & continuous signal added videosignal is produced from the output terminal O of the superimposingdevice 7-8.

The field intensity information Sa is supplied to afield-intensity-to-level converter 7-6 of the transmission-conditionadder 7Tsub and to a field-intensity-to-image converter 7 b-1 of thetransmission-condition image superimposing device 7T. The BERinformation Sb is supplied to a BER-to-level converter 7-7 of thetransmission-condition adder 7Tsub and to a BER-to-image converter 7 b-2of the transmission condition image superimposing device 7T.

The synchronizing signal C.Sync from the transmission-condition imagesuperimposing device 7T is supplied to the field-intensity-to-levelconverter 7-6 and BER-to-level converter 7-7 of thetransmission-condition adder 7Tsub. The outputs Asa and Asb from thefield-intensity-to-level converter 7-6 and BER-to-level converter 7-7are supplied to the input terminals i1 and i2 of the superimposingdevice 7-8, respectively.

The operation of each part will be described. Like elementscorresponding to those in FIG. 11 make the same operation, and will notbe described in detail.

The field-intensity-to-level converter 7-6 produces, from the inputfield intensity information Sa, the signal Asa of which the output level(for example, DC value) is changed according to its condition, or fieldintensity as a field intensity level signal indicative of a fieldintensity level only during a predetermined period in synchronism withthe C.Sync signal.

The BER-to-level converter 7-7 produces, from the input BER informationSb, the signal Asb of which the output level (for example, DC value) ischanged according to its condition, or BER as a BER level signalindicative of a BER level only during a predetermined period insynchronism with the C.Sync signal.

The signals Asa and Asb are, specifically shown in FIG. 69, added inpart of the non-signal VBL period in order to indicate the fieldintensity information Sa and BER information Sb by their levels.Specifically, if the level, or amplitude of the signal Asa is large, thefield intensity level is high. If the level, or amplitude of the signalAsb is large, the BER is satisfactory.

The superimposing device 7-8 adds the superimposed information signalsfed to the input terminals i1, i2 and i3.

FIG. 70A is a block diagram of an embodiment of thefield-intensity-to-level converter 7-6. This converter will bedescribed.

The field-intensity information Sa is supplied to a level shifter 7-6-1,and the output Ha from the level shifter 7-6-1 is fed to the terminal iof a gate switch (SW) 7-6-2.

The C.Sync signal is supplied to an addition position pulse generator7-6-3. The output GATE-Aa from the addition position pulse generator7-6-3 is fed to the terminal c of the SW 7-6-2.

The operation of this converter will be described. The level shifter7-6-1 generates the Ha of a DC voltage level that is higher than thepedestal level of the added video signal, and that is proportional tothe field-intensity information Sa. The addition position pulsegenerator 7-6-3 generates, in synchronism with the C.Sync, the GATE-Asas a control signal for causing the Ha to be superimposed on apredetermined period.

The SW 7-6-2 produces the signal Ha fed to the terminal i as thefield-intensity level signal Asa from the output terminal O according tothe status of the control signal GATE-Aa.

Thus, the level signal Asa is added to part of the non-signal VBL periodas shown in FIG. 70B. The non-signal period can be easily found if it isout of the superimposition timing of the transmission-condition imagesuperimposing device 7T, and thus it is selected to be that period.

FIG. 71A is a block diagram of an embodiment of the BER-to-levelconverter 7-7 for generating a pulse signal of which the duration ischanged according to the BER information.

The BER information Sb is supplied to a level-to-time converter 7-7-1,and the output Tb from the level-to-time converter 7-7-1 is fed to theterminal i of a gate switch (SW) 7-7-2. The synchronizing signal C.Syncis supplied to an addition position pulse generator 7-7-3, and theoutput GATE-tb from the addition position pulse generator 7-7-3 is fedto the terminal c of the SW 7-7-2.

The operation of this converter will be described in detail. Thelevel-to-time converter 7-7-1 generates the pulse Tb which has a DCvoltage higher than the pedestal level of the video signal to which theBER information is added, and of which the duration is changed inproportion to the BER information Sb. The addition position pulsegenerator 7-7-3 generates, in synchronism with the synchronizing signalC.Sync, the GATE-tb as a control signal for causing the Tb to besuperimposed on a predetermined period. This GATE-tb has a widthcorresponding to the maximum duration that the time pulse Tb can take.

The SW 7-7-2 generates the Tb fed to the input terminal i as the BERlevel signal Tsb from the output terminal O in accordance with thestatus of the control signal GATE-Tb, or so that the condition ofGATE-Tb period length>Tb can be satisfied.

Thus, the BER level signal Tsb, as shown in FIG. 71B, is added to partof the non-signal VBL period. The non-signal period can be easily foundif it is out of the superimposition timing of the transmission imagesuperimposing device 7T, and thus it is selected to be that period.

If the BER status is better, the duration of Tsb becomes longer. If theBER status is worse, the duration of Tsb becomes shorter.

While the above embodiment employs the field-intensity-to-levelconverter 7-6 for generating the level signal of which the level ischanged in accordance with the amplitude level as shown in FIG. 70A, andthe BER-to-level converter 7-7 for generating the level signal of whichthe level is changed in accordance with the duration of the time pulseas shown in FIG. 71A, the level signals to be generated in theconverters 7-6 and 7-7 may be changed in the opposite way to the above,or in accordance with the duration and amplitude of the time pulse,respectively. Or both the level signals may be changed in accordancewith any one of the duration and amplitude.

In addition, while the field intensity level signal Asa is added to thedigitized field intensity information signal Sa left as shown in FIG.70B, only the field intensity level signal Asa may be superimposed onthe video signal as shown in FIG. 71B because both the signals arefundamentally the same field intensity information.

In this case, however, when the superimposed information is extracted onthe receiving side, it should be noted that the level or pulse durationindicates the transmission condition.

FIG. 72A is a block diagram showing an example of the construction ofthe time-to-BER converter 7-2Vr for detecting the pulse duration. Thisconverter will be described. This converter is associated with thesuperimposed BER extractor & BER-to-image converter 7-2V shown in FIG.65A.

The video signal Vs′ with the field intensity information Tsa and BERinformation Tsb added is supplied to a trailing-edge detector 7-2Vr-1.The output DT-DOWN from the trailing-edge detector 7-2Vr-1 is suppliedto an AND gate 7-2Vr-3. The synchronizing signal C.Sync is fed to acontrol pulse generator 7-2Vr-5. The output Cu-RST from the generator7-2Vr-5 is supplied to a counter 7-2Vr-2. The output LT-Gate from thecontrol pulse generator 7-2Vr-5 is supplied to the other input terminalof the AND gate 7-2Vr-3. The output Cu-B from the counter 7-2Vr-2 is fedto a latch 7-2Vr-4. The output from the AND gate 7-2Vr-3 is supplied tothe LT-terminal of the latch 7-2Vr-4.

The operation of each element of the converter will be described. Thetrailing-edge detector 7-2Vr-1 detects the trailing edges contained inthe information-superimposed video signal Vs′. FIG. 72B shows thewaveforms of the signals fed and produced.

The trailing-edge detector 7-2Vr-1 detects the ends of pulse, ortrailing edges of signals Tsa and Tsb irrespective of the kind of thetailing edges of the input signal.

The control pulse generator 7-2Vr-5 is responsive to the C.Sync signalto generate the signal LT-Gate that becomes level “High” for the timeinterval from t4 to t5 in which the Tsb probably exists, and the signalCu-RST that becomes level “Low” during the same time interval. The ANDgate 7-2Vr-3 transmits to the latch 7-2Vr-4 only the leading edge pulsecontained within the time interval from t4 to t5. The counter 7-2Vr-2counts only during that time interval to count up the value with lapseof time. During the other time interval, since the signal Cu-RST islevel 0, the counter content remains 0.

Consequently, the latch 7-2Vr-4 holds that counted value just at theinstant when the signal Tsb falls off. Thus, the value proportional tothe pulse duration of the signal Tsb can be extracted.

While the embodiments described with reference to FIGS. 55 through 72Bare related with the transmission of the video signal with thetransmission-condition image signals including the ghost image signalbeing superimposed on the blanking period of the video signal, thepresent invention can also transmit the transmission-condition imagesignals by other methods. For example, the transmission-condition imagesignals can be transmitted, through another separate channel differentfrom the transmission channel using the video signal, from the repeaterstation 53 to the broadcast station 54 or those image signals can betransmitted by multiplexing with the video signal, for example,time-division multiplexing to the broadcast station 54.

FIG. 73 is a block diagram of one example of the transmission of thevideo signal as main data and the transmission-condition image signalsvia separate channels from the relay station to the broadcast station.On the receiving side of the relay station, the transmission-conditionimage signals of 1 H (a horizontal period) superimposed on the verticalblanking period are converted by an AD converter (not shown) of an AD &time-expansion processor 400 into a digital signal, and the fast digitaldata of the 1-H signal is further converted by use of a memory (notshown) of the processor 400 to a slow digital signal of one frameperiod. The next stage, a microwave band FPU (field pickup unit) 203Taas a digital type video transmitter has the function to transmit thevideo signal as main data and the function to transmit the otherauxiliary data. The converted low-speed digital signal (superimposedtransmission-condition image signals) corresponding to 1 H period issupplied to a terminal ACin, as the input terminal for the auxiliarydata, of the transmitter 203Ta, and transmitted therefrom to thebroadcast station.

On the broadcast station, the low-speed signal (transmission-conditionimage signals) corresponding to 1 H period reproduced from the terminalACout of a digital video receiver FPU 300 a is fed to a time-compression& DA processor 401, where it is converted by use of a memory back to thefast signal of 1 H period, and further converted back to the analogsignal by a DA converter (not shown). This analog signal is supplied toa transmission signal reproducer 7Ra on the studio side.

Thus, according to the embodiments of the invention, since thetransmission conditions such as the field intensity, BER and thepresence or absence and levels of reflected waves can be transmittedfrom the OFDM transmission system to other remote places such asstudios, and on the receiving side they can be extracted and displayed,the operator even at other remote places can easily and accuratelyobserve the transmission conditions of signals from mobile communicatorssuch as outside broadcast vans.

1. A digital signal transmission system using a digital modulation system comprising a digital signal transmitter having a first digital signal processing unit producing a digital signal which includes a plurality of signal units, each having a guard interval to reduce multi-path effect and a digital signal receiver receiving a digital signal from said digital signal transmitter, wherein said digital signal receiver comprising: a second digital signal processing unit for processing said digital signal from said digital signal transmitter and outputting a digital demodulated signal and a correlation value signal from said digital demodulated signal; a signal converter, coupled with said second digital signal processing unit and supplied said correlation value signal therefrom, for generating at least a main wave signal level and a ghost imaging signal level corresponding to said correlation value signal; and a display, coupled with said signal converter, for displaying a waveform corresponding to said main wave signal level and said ghost imaging signal level in each horizontal scanning period of said display to indicate a transmission condition in said digital transmission system.
 2. A digital signal transmission system according to claim 1, wherein said waveform indicates a main wave and a reflected wave corresponding to said main wave signal level and said ghost imaging signal level, respectively.
 3. A digital signal transmission system according to claim 1, wherein said signal converter further generates a BER signal indicative of the bit error rate of said digital signal received and a field intensity signal indicative of the field intensity of said digital signal received, and said display simultaneously displays said BER signal and said field intensity signal in association with said main wave and a reflected wave.
 4. A digital signal transmission system according to claim 2, wherein said signal converter further generates a guard interval signal corresponding to a period of said guard interval of said digital signal received, and said display further displays a guard-interval based on said guard interval signal in association with said main wave and said reflected wave.
 5. A digital signal transmission system according to claim 2, wherein said signal converter further generates a time scale signal and said display further displays a time scale based on said time scale signal in association with said main wave and said reflected wave.
 6. A digital signal transmission system according to claim 3, wherein said digital modulation system is a multi-carrier modulation system, said signal converter further generates a guard interval signal, and said display further displays the guard interval based on said guard interval signal in association with said main wave and said reflected wave.
 7. A digital signal transmission system according to claim 2, wherein said signal converter further includes an abnormality detecting unit for detecting an abnormality of said digital signal from said correlation value signal and outputting a signal indicative of said abnormality.
 8. A digital signal transmission system according to claim 7, wherein said signal converter further includes a memory unit, in which the signal indicative of said abnormality is stored and said display indicates simultaneously the signal indicative of said abnormality and said main wave and said reflected wave.
 9. A digital signal transmission system according to claim 4, wherein said guard interval is so designed to be variable in a time period.
 10. A digital signal receiver, to which a digital signal from a digital signal transmitter using a digital modulation system is supplied, said digital signal includes a plurality of signal units, each having a guard interval to reduce multi-path effect comprising; a second digital signal processing unit for processing said digital signal and outputting a digital demodulated signal and a correlation value signal from said digital demodulated signal; a signal converter, coupled with said second digital signal processing unit and supplied said correlation value signal therefrom, for generating at least a main wave signal level and a ghost imaging signal level corresponding to said correlation value signal; and a display, coupled with said signal converter, for displaying a waveform corresponding to said main wave signal level and said ghost imaging signal level in each horizontal scanning period of said display to indicate a transmission condition of said digital signal.
 11. A digital signal receiver according to claim 10, wherein said signal converter further generates a BER signal indicative of the bit error rate of said digital signal received and a field intensity signal indicative of the field intensity of said digital signal received, and said display simultaneously displays said BER signal, said field intensity signal in association with said main wave and a reflected wave.
 12. A digital signal receiver according to claim 10, wherein said signal converter further generates a guard interval signal and a time scale signal, and said display further displays a guard-interval based on said guard interval signal corresponding to a period of said guard interval of said digital signal received, in association with said main wave and said reflected wave.
 13. A digital signal receiver according to claim 10, wherein said signal converter further generates a time scale signal and said display further displays a time scale based on said time scale signal in association with said main wave and said reflected wave.
 14. A digital signal receiver according to claim 10, wherein said signal converter further includes an abnormality detecting unit for detecting an abnormality of said digital signal from said correlation value signal and outputting a signal indicative of said abnormality.
 15. A digital signal receiver according to claim 14, wherein said signal converter further includes a memory unit, in which the signal indicative of said abnormality is stored and said display indicates simultaneously the signal indicative of said abnormality and said main wave and said reflected wave.
 16. A digital signal receiver according to claim 12, wherein said guard interval is so designed to be variable in a time period.
 17. A method of displaying a digital signal transmission condition in a digital signal receiver, to which a digital signal from a digital signal transmitter using a digital modulation system is supplied, said digital signal includes a plurality of signal units, each having a guard interval to reduce the multi-path effect comprising the steps of; processing said digital signal in a second digital signal processing unit of said digital signal receiver; outputting a digital demodulated signal and a correlation value signal from said digital demodulated signal; generating, in a signal converter coupled with said second digital signal processing unit, at least a main wave signal level and a ghost imaging signal level corresponding to said correlation value signal; and displaying a main wave and a reflected wave corresponding to said main wave signal level and said ghost imaging signal level, respectively on a display.
 18. A method of displaying a digital signal transmission condition according to claim 17, further comprising the steps of; generating a BER signal indicative of the bit error rate of said digital signal received and a field intensity signal indicative of the field intensity of said digital signal received in said second digital signal processing unit; and simultaneously displaying said BER signal and said field intensity signal in association with said main wave and a reflected wave on said display.
 19. A method of displaying a digital signal transmission condition according to claim 17, further comprising the steps of; generating a guard interval signal corresponding to a period of said guard interval of said digital signal received, in said digital converter; and displaying a guard-interval based on said guard interval signal in association with said main wave and said reflected wave on said display.
 20. A method of displaying a digital signal transmission condition according to claim 17, further comprising the steps of; generating a time scale signal in said signal converter; and displaying a time scale based on said time scale signal in association with said main wave and said reflected wave on said display.
 21. A method of displaying a digital signal transmission condition according to claim 17, further comprising the steps of; detecting an abnormality of said digital signal from said correlation value signal; and outputting a signal indicative of said abnormality.
 22. A method of displaying a digital signal transmission condition according to claim 21, further comprising the steps of; storing a signal indicative of said abnormality in a memory unit; and indicating simultaneously the signal indicative of said abnormality and said main wave and said reflected wave.
 23. A method of displaying a digital signal transmission condition according to claim 19, further comprising the step of changing a period of said guard interval.
 24. A method of displaying a digital signal transmission condition according to claim 21, wherein the step of detecting the abnormality of said digital signal is the step of detecting on the basis of relative positions relating to said main wave, said reflected wave and said guard interval.
 25. A method of displaying a digital signal transmission condition according to claim 21, further comprising the step of generating an alarm when said abnormality is detected.
 26. A method of displaying a digital signal transmission condition according to claim 21, wherein the step of detecting the abnormality of said digital signal comprises the steps of; dividing a displaying region on said display into a plurality of regions; and deciding whether said abnormality is presence or absence on the basis of the position of said region which said waveform is indicated. 